I think buying links directly from the sites makes it much harder for google to know if they were sold, and google has no issue with web sites selling links, only if they are done for Pagerank reasons only.
" Don"t Try This Be SAFe " Buying Backlinks Is injurious For Websites. Especially from known sellers.
For an established site, it is a huge risk to buy links. For new sites, I think it can be give them an initial push but after the site gains momentum, link buying should be refrained.