I won't buy stuff that has people living in it, although I have bought stuff that had squirrels and mice living in it. Drive by the house, peek in the windows, I have seen many auction properties listed as occupied when it is obvious on visiting them that no one has lived there for a long time. Banks don't know what they are listing, they are wrong about property size, # of bedrooms or bathrooms, occupied status. They literally are in another state and don't know and don't care about the asset. We snapped up a small Cape Cod last year for 140K, the listing did not mention that it was on four acres of farmland with pastures and a barn, we rehabbed and resold it for 395K, made 75K on the deal. If they had put the property size in the listing, and if the appraiser had had a clue, it would have sold much faster and for a much higher price. But...their mistake, our gain!
I always sign the contract "contingent on financing" so I have an out. It is understood you are buying "as is" but you can always contact the local listing broker to see the house before you bid. At this point I just do a driveby, I am more concerned about location, neighborhood, size of house and property than how distressed it is. You make your money when you buy, so you want to buy low enough to have enough margin to cover rehab plus your profit at the end.
Things like oil tanks they generally know about and must disclose. If it has not been reported to the state yet (if there is not an open case # on it), you can have them removed for about $1200. If there is a spill, or an open case #, it will cost more. We had to remove one once and do extra soil testing and I think we spent about 7K total on that. Sometimes you will have a septic report too, sometimes not. We just assume the septic is bad and add 35K extra into our rehab estimate (though the last septic we put in cost 50K--complicated pump up system with mounded leech field due to high water table on site--so the difference came out of our pocket).
Closing is 30-60 days, sorry to be vague on that, but I've only done auction twice, usually buy distressed foreclosures off the MLS, which can close in 30 days as well, all depends on the seller and the title work.