1.Quality - Check clothing for missing buttons, rips, and fading. Anything that you would feel ripped off about if you were buying something at the shops. These things could provoke bad feedback and turn customers off buying your clothing again.
2. Brand- Everyone is brand aware these days. If it was expensive at the shops then it will encourage higher prices at auction. Look at Peter Rabbit.
3. Character- Kids get excited by TV and Movies. Even Adults are getting into the act. If you find Bob Builder, Batman, etc. "It will sell!" at the right price.
4. Price- If your really not sure start at a bargain price like 99c. Use the auction option and bidders will outbid each other to a reasonable price. Or you can check out other auctions for similar items to set the price.
5. Bargain- Sometimes you have the biggest bargain on the internet and it doesn't sell. Just try again. Different bidders are on Ebay every week. What doesn't sell one week can get heaps of bids the next. Otherwise you can give the item to charity and try something else.