what to look for buying lenses on ebay

I've been looking for deals on ebay, but I'm finding a lot off-brand lenses. Are any of these lenses worth while or all they all junk? Pheonix, Opteka and some others. I know that the more expensive, name brand glass is better, but the wallet doesn't support that. Just wondering if any of these off-brands are worth while. If not, I'll just stick with my quantaray and Tamron that I've had luck with so far. thx.

I go by the saying- You get what you pay for.

^^^
Exactly...I would stick with the well known....Tamron, Sigma, Tokina, and what ever brand your camera is...Canon, Nikon etc. etc...
http://www.photography​review.com/Lenses/PSC_​3787crx.aspx is usually a pretty good place to get an idea of how others rate thier stuff.

Try the Kenko. I use them on my S50 and love them. I would probably avoid the ebay ones, as they are the cheaper versions. Try the pro series.