What to look for:

Everyone has specific tastes when they are looking to buy well worn/trashed/used items. Many times people will be sucked in just by looking at the listing. Other times it's a seller's reputation, correspondence with the seller, etc. There are main things that you need to be aware of when buying well worn/trashed/used items.

1. Check your seller out. Does anything seem off kilter? Too many bids at once? Too high of a bid for what you are buying?  It's hard to know since most sellers have their auctions set to private. However if you watch the bidding & pay attention to how & when the bids are placed this helps.
2. If you are contacted by the seller while bidding and they are offering you items/pictures if you bid higher this is basically like shilling & isn't fair. If they are offering this to you then chances are they are offering it to another bidder too. It creates a bidding war and the only people who profit from that are the sellers. It's underhanded & unethical. Ex: If you bid XX.XX I'll send you 5 free pictures with your purchase. If you contact a seller that you are interested in they will usually set up another auction specifically for you with the items you want & a price that's already agreed upon.
3. If your seller has a ME page it's a GREAT place to get to know the seller's personality & who you are dealing with. If a seller has a legitimate ME page it will talk about the items they offer & possibly a bit of background on the seller themselves, along with more pictures that may or may not be allowed in the listing. Occasionally you'll come across a few that bash other sellers. To me it shows that the seller has no Integrity in what they sell. If your seller can't get you the buyer with their product, bashing other sellers most likely won't help.
4. Some sellers also request that you ask for full pictures of the person you are buying your shoes from. In most cases most sellers will do this. In some cases there may be legitimate reasons why the seller won't do full pictures or if they do they will block their face out. There are so many sellers who sell well worn items and it could jeopardize their '9-5' job, who have teenage kids that don't need to see their parent selling in this category.
5. There are also sellers out there who are buying knock off shoes at Goodwill & putting them up as their own well worn shoes. This is rediculous. It's easy to tell (especially with flip flops) when the toe prints don't match up. If the toes don't fit, that seller didn't wear it.
6. When you see sellers with 8-9 different shoe sizes, that's when the alarms should go off in your head. I myself can wear anywhere from a size 9-10.5 it just depends on the make, style & brand of the shoe. That's considered 1 shoe size from 9-10. Most people don't count the 1/2 sizes. In other words if you see someone listing size 5,6,7,8,9,10 for shoe sizes..then you are guaranteed that the seller didn't wear them all. However if they mention that they are selling for friends then most likely they are. (this is where the toe prints come in handy)

Shipping:

There are a variety of ways that sellers ship their items. Many times it includes extra's not normally related to regular selling. Check your sellers ME pages to see if there are any hidden costs. Please remember that insurance is to cover the SELLER's behind. As a seller it would be MY responsibility to get your package to you in the same shape and form that it was represented in the auction. Also remember that it is against ebay's terms to OVERCHARGE on insurance. However there are many sellers that do this. Ebay's Terms of Service for Shipping 

USPS Priority Mail Insurance Rates:

Fee . . . . . . . . Insurance Coverage
$1.35 ................ $0.01 to $50
$2.30 ................ $50.01 to $100
$3.35 ................ $100.01 to $200
$4.40 ................ $200.01 to $300
$5.45 ................ $300.01 to $400
$6.50 ................ $400.01 to $500

Feedback:

Feedback is optional & if your seller has a name that makes it very obvious (even if the auction is private) to others of what you have bought it would be better to start up another ID. For instance you don't really want Aunt Sally to know that you buy used/well worn/trashed items?

In closing:

Not all sellers are 'bad'. You just have to decide which seller works best for you. There are quite a few out there now to choose from which is great! It keeps the competition alive & assures you that you will get what you paid for. Afterall, if 1 seller doesn't meet your needs there is another one who will!