There's a few things you have to know/watch on eBay. First is the sellers feedback. You don't want to buy from a guy with a feedback of 3 and under, or from somebody who has a lot of negative feedback. If you read the negative feedback you learn what the seller is like, and sometimes the buyer.
I'd do it if I was confident in the seller and knew he wasn't selling you pirated items.
Can you trust ebay Photoshops? Like are they all pirated? Because I see some as cheap as $150 there.