Offering in appraisal section:
If appropriate appraisal is given and then offered to buy, no punishment
If inappropriate appraisal is given and then offered to buy (could be though of as scamming), temp suspension (maybe a day or two). repeat offenses = longer suspension
If it's a plain out offer... I have no freaking clue
Spamming multiple threads:
Warning first. If continued, threads are closed. If still continued, thread creating rights are limited for a short duration (if you can find a way to do this)
Flaming:
No idea. but mostly depends on how bad it was
Negatively affecting others business:
Warning first. If continued, short suspension.
As for what to do with people who offer extremely low amounts, I believe that as long as it's in the selling section, there should be no punishment for it. I mean... it's the seller's responsibility to know how much to sell for.
As for people who don't honor auctions, I think taking away thread creating rights for a short duration is satisfactory. It's the seller's responsibility to set proper s/o's, b/o's, times, and increments. If they're not satisfied with their current bid, then they should have made the s/o higher.