Theymos should probably consider tweaking the algorithm slightly. 'Micro-transactions' or deals of small amounts probably shouldn't count for much if anything at all and certainly shouldn't be giving people a +1 or 'green' feedack because it just leads to users seeking out doing certain deals as cheaply as possible purely for the feedback. As for escrow deals, maybe neutral feedback would be more appropriate.
Or even free "transactions". I've got some positives on another forum for giving domain names to other members without charge. They were names that I was going to let drop, so they were of no value to me anyway, but they have given me a positive rating. In this case the rating is really a bit meaningless.