While a "winner" at auction in my county has 30 days to make full payment, the challenge comes in finding a lender who will lend on a property they can't appraise on the inside (since access is not granted until the deed is received).
In my county, delinquent tax auctions and foreclosure auctions are held at the same time. In the foreclosure auction your biggest competition is the mortgage holder, so it really could be a sucker's bet. In my county, 95%+ of the winning bids are by the banks.
The delinquent tax auctions are another matter. Very good deals there - but sometimes a waste of time when you find out the homeowner of the only property you were interested in paid the back taxes that morning. And the tax auctions are last so you have to sit through 60+ foreclosure auctions before they get to what you are interested in. Luckily, most of them go for the minimum bit (2/3 of appraised value) since few people want to get in a bidding war with the banks.
Every once in a while (like this past week), a bank's rep (usually a lawyer) won't show up and you can snatch a good property for the opening bid.