If you are buying at auction, you won't be allowed to use the scanner anyway.

You will be lucky if you get to look at the MIL light.

Edit to comment: Watching them drive by is more than most auctions. Looking under the hood while they start the engine to prove it starts is often the most you get.

You don't need the best OBD reader, just one that does the job. Buy a cheap one that works for OBD II that is CAN compatible and also gives trouble code definitions. The $50 Innova scanner that Walmart sells will do that. If I just saw any trouble code, that would reject a car I was shopping through.  Don't buy problems and take an experienced mechanic with you. Auctions are full of junk anyway.