I give them a warning.. usually filled with sarcasm.. if they don't get it after that their loss... I upvote comments on my posts.. the value is determined by the quality and relevance of their comment... spammers get nothing... habitual spammers get flags instead of upvotes... although I hate flagging people..

My thought is that when they notice their comment was .01 but I upvoted someone else to .22 that'll get the point.. pity da foo if I have to point it out to them..