If you just post a single destroyer on all your planets and said Sapper didn't have some of the trade skills, would their harvs just get blown up over and over? If you started a war with them... So I suppose you'd have to notice first huh.
Edit: just revisited that post about not taking from colonies you don't own (I.e. No sapping)
So if you tried doing that you would end up trading with them then? Could you give us some numbers on how that works?