I mean, it's difficult to manage that, but if you're trying to put something new in the game just for the Supporters, it would make sense to just ask them in order to get them happier.
You could do that. You'd be ignoring the fact that the majority of people aren't supporters, and it would be a pretty dire game if there were only supporters left, which could happen if advantages are given to supporters, which autobid would clearly be. You're also ignoring the fact that every non supporter could be regarded as a potential future supporter. Giving massive advantages to supporters will not make potential supporters more likely to buy.
Signed: A Freeloader.