This is part of why I avoid buying these on ebay.

Vendors with established sites or Amazon accounts get to build up a reputation of their own or for their lights. Some of the better vendors, like fancyflashlights/cnqualitylights, have responded to requests to check current draw on their lights. The provides a very good indication of actual light output. They also tend to post more pictures, particularly those of the beam. Some sites like DX even has reviews and comments, which really helps provide notice if the quality of a particular item changes over time. This allows me to play it safe unless I try to be an early adopter. Even so, being an early adopter is pretty safe when dealing with a good vendor that provides beam shots, current draw, and their own impressions. Some of the worse vendors like dinodirect, for example, responded to a post for pictures showing a SST-50 label on their reflector, but everyone got lights with XM-L labels on the reflectors...they were XM-L.

With ebay, the sellers often sell so many different items that it's tough to tell if they're slipping in a bad product. Not to mention the pressure to give good ratings, and that those ratings are for the seller, not the product.

Finally, it's good to participate in online discussion about these lights. This forum is good. So is budgetlightforum. At blf there's a forum just for vendor feedback. It's not like cpf where your posts will get deleted or you'll get banned if you write anything bad about a contributing vendor or manufacturer.