1) Pay on a net-30 basis, so that in most cases publishers send two months of traffic before they are paid;
2) Wait until the last minute before a payday to claim a policy violation so that the maximum amount of traffic that the network will refuse to pay for is sent; and
3) Make the description of the policy violation so vague that a successful lawsuit is nearly impossible without significant pre-trial discovery efforts, which will be aggressively fought by the phalanx of attorneys employed by the ad network.
What should be even more concerning to publishers in Google's case is the new "Valuable Inventory" policy [2]. In a nutshell, this essentially says that Google is the sole judge of whether or not your content is good enough to display ads against. If they decide at any time that it isn't, you will be banned and your earnings will be withheld. They've also implemented a policy forbidding ad placement that pushes down the site's content - an impossibility on mobile devices. The aim of all of this is to make all publishers technically in violation of one or more policies, which gives them unilateral discretion as to which publishers they choose to pay.
It's sad, but not altogether surprising, that Google and Facebook are acting in the same underhanded way in the operation of their ad networks. The only way to avoid this kind of behavior is to use lower tier ad networks, which sadly produce lower RPM.
[1] http://www.businessinsider.com/google-search-ad-policies-cos...
[2] https://support.google.com/adsense/answer/1346295?hl=en#Ad_l...