You'd be surprised how easy it is. It's just that most managers decide to ignore it as long as the posts are of decent quality.
Agreed.
If they really want to weed out the farmers all you have to do is ask them to create accounts on your site and withdraw from there, but I don't think it's worth the time.
It can also be overcome using VPNs and multiple BTC addresses. Then user can sent BTC from address-2 to few truted sites and withdraw to address-1 from them after 1 or 2 days but not at the same time.
P.S. Taint analysis of addresses would be better but it is hard and most of the managers won't do it.
-MZ