In my experiences, here is the hierarchy of Facebook effectivenes:
1. To generate likes
2. To generate traffic
3. To generate leads/ sales
If what you sell is daily ordinary products with affordable prices (such as clothes, shoes, accessories, etc), then it might generate leads since the purchase is easy and low risk. But if what you sell is niche service or products that only specific customers could afford to buy (like web design service, business consulting service, industrial machine spare parts, etc) then Facebook ads perhaps is not a good idea.