Mecum Auctions- Pricing
They aren't going to give it more than a visual inspection. Probably decode the vin. The high end cars tend to have corroborating evidence of some sort as to their authenticity, pictures and docs on restorations, etc. The low end cars are going to be "as is" and you will have only what the owner says, just like any other car you would buy.
I watched a behind the scenes type piece on a guy buying a car at an auction and he happened to find an oil service sticker in the car, he called the shop and was able to get a full repair history on the car which was quite extensive.
I've never even been to a Mecum, but it is easy to assume that logistics and time would prevent them from doing much of anything to check on what the seller claims on any cars unless they are likely to sell for over $75k.