Ive seen this several times with my sites....over the years. I havent changed anything with my site....and my pay per click drops from 6-10cents to 1cent and sometimes 1/2 a cent per click. so what the?? Thanks for any feedback!!
Buying traffic is actually against adsense TOS. Since you are paying google to send traffic to your site, this can happen. Not sure though. Try targeting your campaign only to US/Canada and see if the EPC increases.
might be smart priced by automatic triggers, Google products that wont ask about permission between each other and seems so far is connected more then you think, they are dating in fact.
I don't think there is any penalty to buy traffic. It all depends on traffic quality. If advertisers are not making money, they will not pay you top dollars.