I totally agree with you about those handmade promotion sites. A lot of them seem to be like for a like, which aren’t the kinds of likers you want on your page because chances are they aren’t interested in your stuff, just your returned like. I lost under ten likers in the FB cull recently, I think because the majority of my likes have been organic.
I don’t worry too much about the ads. If you search anything on the web nowadays, you’ll suddenly find it popping up in the ads when you’re in your email, or on other sites. So I think they’re all at that trick, not just FB. I’d never use the internet if I started worrying about that
Edit. I must just add a quick shout out for @dottiedesigns’s British Crafters on FB as a sensible and well run promotion site. I’ve definitely had sales directly from using the site, and I know there are non-selling customers popping in for a look over there too because it’s a nice friendly site.