+1 on mostly everything on this topic. Ash-Bash... probably the best post I've seen so far from you.

One thing that you can do for yourself is to include your eBay profile page link so that people CAN see that you are a guru and that you aren't just making things up. Plus, I believe you require a bank account and/or credit card to establish a PayPal account, which in the US, you have to be 18 to snag the plastic. (I'm not sure if there's an age requirement for an individual bank account.) As you've said, credentials.
I'm simply amazed at how crappy some auction listings are on eBay... next to CraigsList for being uninformative, uninteresting, not enough or too much information, etc.
I will support most of Ash-Bash's points because I use the same things to make sure that I sell my stuff. I am not an avid seller and I do not live off of eBay, and most people that do sell on eBay are doing it to get rid of a few odd things or to try to establish an online business. A few things to consider in addition, however:
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When Ash-Bash said research, I think he meant to look at other listings to see what they say, what the descriptions are, etc. However, I look more into it than that.
I start by knowing what I'm selling. As silly as that sounds, it's important to know what exactly you are selling. If you don't know what the heck it is, what condition it's in, what the history of the item is, any damages done... you can't really describe it very well or even do any research, can you?
We'll go with the example of an iPod. On close examination, you will find out that it is an iPod Photo, fourth generation with 30GB. This is much different than an iPod Touch, second generation with 8GB, and so forth... a multi-hundred-dollar difference. You need to know this stuff so that you can set a realistic price, be able to describe your item so that buyers will know what they're looking at, and the more they know, the more interest you get. No one's going to spend a lot of dough on something they have no clue about, and the fact that they can't hold it, touch it, try it, or test it makes the mystery harder to unravel... something you're going to have to do for them.
Another important part of research includes knowing what your auction price will be. I personally like to offer my items as an auction because it gives people that interest to bid for something for the possibility of getting it cheap. Be realistic. The person that wanted me to sell his iPod Photo told me that they were selling for $120. He was correct... to the extent that they were being offered on eBay for $120 for Buy-It-Now. Auctions were ending at $30-$50 for these things. Now, pretend to be a customer that wants an iPod Photo 30GB. Would you want to pay $120, or try for $30-50, maybe $60?
Exactly. Be realistic.
What I do with this sort of research is to search for the item I'm selling, then placing similar or exact items on my watch list to see where the auction closing price is at. Once I establish a trend, I shave off a bit of that price and start my bidding price at that amount. You COULD be adventurous and start at $0.01, but I like trying to make a return on my investment. No seller likes putting an auction out at a penny and then turns around to see that their $100+ item sold for a mere $4.51 because no one was interested enough in it.
Another thing is interest. Is the eBay market looking for what you're selling? Everyone is dumping their iPods on eBay, but are people actually buying them up? From what I'm seeing, even people are wanting to snag iPod Photos, but for cheap. So there is a market, but it's competitive and we're not going to make much from it. It's your call whether to even try or not.
Watch how people are doing their shipping. Free shipping is always a nice thing, but we all know that shipping isn't free for us. So make it work for you. Like I said, I always take the closing price of the trend and shaving a bit off and starting it from there. It helps with making a decent amount off of my item and shipping doesn't really kill me with the items I sell. But it's your call. Remember, people are trying to snag a deal. Charging someone an insane amount to ship an item will turn most people away.
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Now, back to the item.
When putting up your listing, I agree and disagree with Ash Bash on headlines. You don't need a subtitle, but it can help if you make use of it correctly. An extra $0.50 won't kill you, but utilize that space well. You only have so many characters in which to insert keywords.
Which brings me to my next point.
When people search for items, there's a common search term. "iPod" would be one. "new" works. Even specifics are helpful for people who like to refine their search terms, so "30GB" will really assist and highlight your listing from others when punched in as a search term. There are problems, however. People mis-type and misspell things... including you. Don't misspell your item headline... that's just inviting a savvy eBay user to steal your item for less than nothing, or it invites no one at all because no one is looking for an "iopd." Double-check your spelling. Also, someone looking for "30GB" may not actually find your listing with "30 GB." See where that might be a problem?
You can also use CAPS LOCK FOR YOUR HEADLINES, but I see it as childish and dumb. On eBay, it doesn't matter as long as you can attract some attention to your headline. Use at your own discretion. I rarely if ever do.
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Now, does the item have any scratches? Any bumps or bruises? How old is it? Does everything work? Are all the accessories included? Looks like the finish has some minor dings and scratches to it. That and I only have the charger cable and nothing else. PUT THAT ON YOUR LISTING DESCRIPTION. I also disagree with Ash-Bash on technical jargon. Keep it simple at the beginning of the auction, but put technical specifications at the bottom of your listing so that it is easily accessible and again, the buyer will know what he or she is buying.
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Take pictures of everything that you're including. Put down the history of the item, to include repair work, what you usually do with it, etc. Honesty builds trust. Trust builds interest. I personally take pictures of everything included, then zoom in and take detailed pictures to show any scratches, dings, scrapes, etc. And take good pictures. A blurry photo does no one any good. A low-resolution photo is just as bad. Aim for at least 800x600 so that the customer can actually SEE what he or she is buying. Post every good picture that you take, and offer more photos if buyers want them. Encourage questions about anything from the item itself to shipping to special arrangements. Accommodate to the best of your ability without risking yourself to dealings outside of eBay/PayPal. Oh, and do not take anything other than PayPal! This is to protect you and the buyer. There is no reason not to... both parties are protected if something goes awry during the transaction phase.
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I also disagree a bit, but not much, about adding personal information to "spice up the auction." No one cares about you on eBay or about your personal story. They are there to buy something. They MAY want to know why you're selling "such a great item." If it is so awesome, why are you selling it? Always put yourself in the role of the buyer before you make up your listing. Putting out extraneous information on your auction listing may turn people away too. As long as it is relevant to the item, it would be safe to include it. Otherwise, you can do without it. Then again, that's just my opinion.
I'm also skeptical about the part where Ash-Bash mentions to ask for a sale. That's up to the buyer, and you don't want to try to coerce anyone into anything. Would you like to be pressured to buy anything? Then again, how do you do that on an auction listing with no immediate interactivity? Maybe if you were creative with your words and "show" how that particular item can be useful to the buyer, then yes, you can do that. However, most people on eBay know what they want and this kind of becomes a moot point.
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Basically, Ash-Bash was on-point with most of his tips. Just keep in mind that you are dealing with a real person on the other end, so present your stuff as such!
@Ash-Bash: As far as an e-book goes, good luck with that. I think most of these kinds of tips are available for free, and if not, you and I just provided a bunch of tips here. But carry on... you probably have a ton of unsaid goodies that you're saving up for your e-book.