Buying at auction (at least here in CA) you typically don't see the inside of every house you buy. You also buy it with cash, the same day that you find out how much you can buy it for. So, you either have to be comfortable with that or not participate.
How do you get "comfortable" with that, you ask?
Well... there's lots of contextual clues.
How old is the house? How big? What does the outside look like? What does the lawn look like? Are there cars on it? Couches? What do the cars in the surrounding neighborhood look like? What do the people in the surrounding neighborhood look like? Was it previously listed on the MLS? If so... how long has it been and how dilapidated does the outside seem from when the photos are taken?
After a while... you'll get to the point where taking in all of these things is second nature, and you won't really need to see the inside to get within 10% of the right number for rehab.
Then again, you'll also be very, very, wrong 10% of the time. So if you can't afford to be, figure out a way in.