8 days.   If you set your blocks to exclude serial NPBs you up your chances of having them unable to bid. As you seem to attract NPBs I assume your listings attract them, or you don't have the available blocks in place.   Auctions are so noughty.

I have blocks in place but as I have mentioned a lot of them that slip through have very low feedback. This leads me to believe they merely create a new buying account after they rack up the strikes.

I sell BIN items (have only sold the odd item via auction). I think auctions may attract many buyers that are in it for the thrill of the win, the excitement of nabbing a potential bargain. After the win, their enthusiasm dissipates and the seller is left with a non communicative buyer...