hey again...read this thread and thought I'd pop up here.
This is how I got a lot of my gear...two reg/octo/gauge setups, a bc, and a tank, all ex-rental/class equipment. It's served me for at least 5 years, or most of the time I've been diving, and it set me back not a lot at all.
BUT
It's all Dacor gear, for one thing. My first reg, an Enduro (like the one I trained with), is now essentially a paperweight, since Dacor is no longer acknowledging its existence. Who knows how long it will be before my Viper Tec goes the same route. It's not a BAD reg, I guess, but I don't much like it anymore...it freeflows occasionally too. Also, since all this stuff saw heavy use before I owned it, it's already quite worn around the edges and beyond. My Nautica BC is now Swimming Pool Brown (TM), fabric things are coming loose, the cummerbund is not really adequate, etc. My reasons for looking for new gear is just that my old stuff is worn out, the service situation is questionable, and dang it I just wanna get something new.
Lesson: ex-rental gear can be a great way to pick up gear cheaply, esp. if you're a newbie searching for your own first rig, but remember that it's not just used, but USED. And make sure that you will be able to get it serviced down the road if you intend to keep it for a while (THAT is why, for chrissakes, don't buy anything Dacor--at least if it's used).
I imagine ebay would probably be a crapshoot, although if you know what you're looking for and don't get caught up in Last Minute Bidding Frenzy, I'm sure you could walk away with something serviceable (in both senses of the word).
cheers
Billy S.