If you really want to hurt the shills..
Slowly restrict the amount of IP's they can post from; Increase the chance of creating "recalcitrant employee's" whos clumsiness costs them subnets and further twist the dagger of their demoralizing outcome until every post they make is saturated with hesitation and fear.
With no ability to post, they have no ability to make money.
With no feedback from their posts, they have no ability to refine their approach.
Deny them sustenance. Deny them growth.
; )