I have screen shots, but of course that doesn't prove anything. But I can see that especially the account 'btsshr' always magically changes and outbids a lot of orders in split-seconds on the bitUSD/bts market, at least mine.

It might technically be possible for a human to delete and make a new order during the same block, but I think it's highly unlikely.

I'll see if I can find some concrete evidence on cryptofresh.