It all depends on the auction. My old firebird came from an auction and it was the best car i'v ever bought. the engine went out on me but 100K miles in 3 years takes a toll on an engine. One of my previous fiero's came from an auction. I dident pay a lot for it but it was a big pile of sh*t. it got me around for about a month than took a dump on me. I was going to engine swap it but ended up just parting it out and making somer money back off of it. my sugestion is when you go bring a mechanic or someone mechanicley inclined with you to look over the vehical. auctions are a real 50/50 deal. your going to get a good car or your going to get a heap of junk.
And as far as salvage and rebuilt title's go. Newer vehicals stay away from them. Some INS company's wont insure them and when you go to sell them the resale value drops through the floor. Rebuilt means the vehical was at one point a total loss and headed for the junkyard. Someone bought the vehical and rebuilt it.
They do need to go through a very strict inspection that varry's from state to state to obtaine a rebilty title from a salvage title.
I have bought 2 fiero's with rebuilt title's and the reason i can get away with them is 1 my ins company will insure a rebuilt car and 2 fiero's resale value has already dropped through the floor and parting them out i usualy get more out of them than i paied for the car.