Just a guess, and I have some free time to do some research. Multiple accounts, with the same person behind them, even if it's not shill bidding or anything improper, are grounds for immediate suspension.
Since some people here have dealt with one or more of these sellers, why not email them and ask. Maybe it wasn't anything they did, but someone else, and it made them look bad?

I too have been second bidder, at the last seconds, by small amounts over my Max. bid. (not casino items)