Sheriff's sales probably vary somewhat according to what state you're bidding in, but I can tell you a few aspects re sales in NJ, some of which would surely apply more widely (but as always, YMMV).
The vast majority of properties at these sales in NJ go back to the lender via a $100 bid, and there is a good reason for that. The lender has an "upset price", which is usually the amount owed on the property, including all of the costs of the foreclosure itself, which can be higher than you might imagine. So the lender will bid in itself if the bidding doesn't reach the upset level, in effect taking back the property. If no one bids at all (this is generally because the investors at the sale have all determined that the upset price is greater than the value they're willing to mentally assign to the property, esp. w/all the unknowns of sheriff sale properties), then the lender bids $100 and takes the property back. All of these REO's, or lender-owned properties, are the ones you see on the multiple listing service months (or in NJ, it can be years) after the sheriff sale.
The few properties that get the investor bids are the ones in high-value areas, where the value of the land alone almost justifies the purchase.
Another investor play involves more research. This move considers the position of the lender who is foreclosing. All mortgages coming after the foreclosing one are wiped out by the sale. Therefore, in theory, say if you found a property with a very low first mortgage which is being foreclosed by the lender in 1st position, you could bid in at anything over that amount and get the property way below its true value. In reality, of course, it doesn't usually work out that way. In my example, a lender in, say 2nd position, would bid the amount of the lst mortgage and up to the amount of its own mortgage. 2nd position thereby captures the value differential for itself, rather than just sitting by and watching its mortgage get wiped out by some investor who's going to benefit by that amount. And while we're talking reality, a property like this would only rarely make it to sheriff sale, for reasons you could probably work through in your own mind more quickly than I could mention them here.
I'm not trying to be a Debbie Downer on your idea. Just asking you to keep in mind that these are all cash purchases, so taking cues from the investors who attend these auctions might be instructive. They're aware they would be broke very quickly if they took on most of these properties, so they take a pass on the majority.
FWIW, I hope you wouldn't mind a respectful suggestion. Maybe attend a few auctions just to observe before laying down any of your precious money. I wish you luck.
