I'm sure there will be plenty of attempts at feedback manipulation however from doing a bit of thinking in most cases it makes absolutely no sense to even try. As we have seen, poor feedback doesn't stop buyers from buying and the rewards (Powerseller 15% discount) are not of enough value to outweigh the costs to manipulate the feedback.
For me to get to the 15% discount level I would have to spend more money than I would receive as a discount. I think it's much easier just to sell more and do a better job of it and let the better feedback come naturally. Come to think of it, adding a Dollar to 10% of my listings and/or increasing my handling charge by 25 cents will get me the same financial reward. This is a lot easier than some complicated feedback scheme.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.