Hmm... I don't know much about them. They have a wiki page:
It looks like they are an affiliate marketing company. I don't think they are a scam, but the references in the wiki page says (the link to the blog post it's referencing is broken), "Kellie Stevens (August 20, 2006), ShareASale was about to become the largest Affiliate Network company but they terminated a lot of affiliate accounts without even notifying and paying them commissions. Now ShareASale is a small company with few merchants."
I guess they've had a lot of ups and downs, but I don't think they sound like a scam (maybe they were temporarily a scam-ish thing back in 2006 to all the terminated profiles??). They've been around a while, so that says at least a little something... I'm guessing they might be kind of like Amazon Associates where you get a link to a product that you can share with your audience. ^^