as long as the back links are there is no problem and if the directoryowner is willing to spend some money on it its okay!
I think every one should learn to research very carefully what links they buy. When I first started buying links I did not know a lot about how to research the quality of the lin I was buying and bought some I should not have. In time every one learns how to be more selective and research each purchase better. The unfortunate part is that their are always new people just learning that can be preyed upon. There is not much you can do to stop the people who take advantage of them besides learning how to spot them.