I've experience buying repo vehicles at both offline and online auctions.
I agree offline auctions can be a risky business. You need to know very much what you're doing, or you may end up with a vehicle in bad condition and with a price not nearly as good as you could have gotten. Remember you'd be competing with professional car dealers with lots of experience.
Online auctions, on the other hand, are much safer for someone new, provided you take the necessary precautions. You should always get or ask for a full Autocheck - my favorite - Vehicle History Report ( not the one you get for free, sorry ). Ask any and all questions you may have, speek to other buyers and check the seller's rep. Don't forget also to find out how much similar cars have gone for in the past, and bid accordingly. There's a lot of money to be saved if you are smart.
Here's a pretty good article on repossessed car auctions .
Good luck!