Very little. When I was younger growing up in Australia, auctions were very common, and it was very much the "traditional" model, everyone stands around in front of the property and puts up their hand to bid.

Regularly auctioneers would get caught taking bids from trees or vehicles to push prices up. They'd get caught when their fake bid was the highest. It became so common it was almost expected, and reforms to the process had to be introduced.