I sell most of my items as auction, because they seem to sell better that way. For clothing, often you're best to sell as a buy it now with immediate payment required.

Also, set up buyer requirement blocks, to stop people buying who have had 2 or more non payment strikes against them in the last 12 months (It's a rolling 12 months). https://www.ebay.com.au/bmgt/BuyerRequirements

I would also add those buyers to your blocked buyer list, which should be on the same page as the above link. Be sure to cancel the transactions, stating non payment, so you get your fees back and the buyers get a strike on their account. If you don't cancel, you will still have to pay ebay the fees.