Depends on your state. You will definitely need a dealer's license, which in my state, is an adventure unto itself.
After that, you just need to check with the auction to see what they require for you to purchase or sell there. Some auctions are for franchise dealers only (e.g., Ford or GM dealers) and independents can't go.
The next thing you will need is some knowledge and experience. There is no book, no class, no online reference that can even come close to what years and years of experience in the car business will teach you.
It looks like some wholesalers just ride around and hustle a few cars a month, but there is nobody who does that who wasn't already in the car business for a long time before.
If you get as far as getting a license and going to auctions, remember to always wait for the "sure thing". Don't just buy something to say you got it. Always wait for one you just KNOW you are stealing at that price. That's where most dealers get into trouble....they want to have a lot full, and they want it now, so they buy some cars that aren't that great a deal.....they they get stuck with them and ultimately lose money.
I personally will get my dealer's license within the next year or so, but I will only buy cars that I absolutely know that if push comes to shove, I can sell to a local dealer and at least make a few hundred.
Never get stuff that you have to sell at retail to make money.
Example: 2 years ago, the dealership I worked for was buying Explorer Sports with 15-30k miles, for less than 10 grand. Sometimes 8-9 grand, depending on the options.
We were selling them all day long for 12-13k.
So if you, as an individual, could buy them for say, 10k, and turn them quickly for 12k, that's 2g's, in your pocket, minus expenses...which are minimal on a car that new.
Same for the so-called "program" cars, mostly Tauruses. They could be basically stolen at auction, then sold for lots of profit.
Always stick with the hot seller, no matter what it is.....don't buy something just because you like it. Buy it because you can make money on it.