They themselves deleted their own posts, imo. 

You can do this through your member account by clicking on the 'Edit Account Information' link in your member name header.  Then at the very bottom of your settings there is an option you can select misnamed 'remove all messages from this user'.  I say misnamed because I used this option once, believing it meant 'delete private messages'.  The option should be re-named 'Delete all your forum posts'.

I guess some of the paid pumpers are clearing their tracks...