I hope no-one minds if I close this thread. The only reason being - too may different viewpoints could end up killing the whole idea, because people might be scared of offending other people, and list elsewhere. I like Mike's suggestion, but I also respect those people who want to do the auctions their own way. So please allow me to make a final decision as follows (I'll close the topic off in about 24 hours).
MTM's rules are the official and recommended standard, and will be posted in a sticky topic at the top of the G45 Supermarket.
but
If you don't like those rules, you can do it your own way with your own rules. Everyone will be responsible for their own auction results and for any disputes that may arise from them.