Captcha verification can cut down on a lot of the bullshit.
If they're not legit, your blog is probably getting scraped due to the nature of the content.
Selling links is for chumps. If you have decent traffic, sell ad space. You can bill per click or number of unique impressions and you'll be working with more of a revenue stream. Anyone who knows what they're doing is not going to pay much for a PR4 link, especially of there are other outbound links existing solely to pass flow.
If they're not legit, your blog is probably getting scraped due to the nature of the content.
Selling links is for chumps. If you have decent traffic, sell ad space. You can bill per click or number of unique impressions and you'll be working with more of a revenue stream. Anyone who knows what they're doing is not going to pay much for a PR4 link, especially of there are other outbound links existing solely to pass flow.