I have to imagine it's not the amount of feedback.

Before I started using amazon to sell off (and it's rare when I do) my unwanted tpb's I used to use ebay years back. I always got my money promptly and I had no feedback practically.

I suspect it's a dollar denomination then. Or policy has changed.

They probably figure noone's going to get too mad out of being swindled for a few bucks, but start pushing the triple digits and tempers fly I guess.

Me, I get mad when my local grocery clerk rips me off a penny even. But, I'm a cheap bastiche!