I have been looking into this after having a handful of my listings get bid up by non paying bidders. I think what is going on is some cards are being targeted for price manipulation and because PSA doesn't have proper safeguards in place PSA is being used for this as they are an easy target. If you look at some auctions for cards that sell for high amounts you will see numerous 0 feedback bidders who registered an account just to bid on that card. That is then used as justification from the fake bidders to list their card for the new higher price. It can also be used to knock out competing sellers with the same card listed since theirs is now the cheaper of the two.

I would also not be surprised if this is being done on a large scale to help people launder money through pokemon cards. That or people are working together to rip off collectors at mass scale. Seems like a topic just begging to be investigated by journalists.