Would be great if adsense could share with publishers the spam rate per ad channel (or even better per ad unit)!
So far, for a publisher (aside from asking one's adsense manager) there's no direct way to know the spam rate of a channel (or even of one's account). Sure you can kind of guess following smartpricing or if you see high ctr/low earnings, but that's just a guessing game, and you can't really fix it for sure without hard data to rely on.
I guess adsense is reluctant to share spam rate because they're afraid some publishers would outsmart them, but hey, google is a behemoth, am sure they'd still find a way to corner the black sheeps (and it would one more step toward their ultimate AI).
If adsense really wants publishers to lower spam rate and provide with better traffic they should reveal those data to publishers so we can improve our sites (ad positioning, or even content) in rational fashion.
Hope someone from adsense will hear me!