One team that used to operate at Tring were all from the same family. The women used to do the "knocking" during the week, basically ripping off people on the doorstep by undervaluing items, and the men would all troop in to the most local auction house at the weekends and sell them.
Their shillers were all close relatives, who nearly all wore small trilby hats (like Boomers haloween one) so were easily spotted by auction staff.
The word would quickly go round and the same thing happened to them. They would end up not only buying their own goods back, but paying buyers AND sellers commision.
It gave everyone a good laugh when it worked, and discouraged them from returning too often.