Purchasing likes might add to your credibility to new facebook page visitors, but those purchased likes will not be customers at all. And obviously, it will not be legit unless the likes are generated by a facebook campaign itself. But you are of course to do as you please, until (if) you get caught.
I have found facebook ads useful to get more visitors for my niche websites. But I agree that for businesses it might be less useful. I am planning to create business campaigns soon, so I will see how that turns out.
But for my niche markets, at a low 0,02$ per click, I made over 1000 people like my page in no time and it certainly made more people visit my websites as well. And by some effective adsense placement on those websites I am even making a slight profit.
