When buying links for sites that really matter to you (you can't afford to lose them or screw them up) buy only from providers that you've already tried and saw the overall results. I'm always tracking my results from my own PBNs and the PBNs links that I've purchase. After tracking hundreds of keywords for tens of different sites for more than a year I can tell you that getting backlinks from particular sites can fu*k up your site unrepairably, the anchor ratios and other BS doesn't matter in this case, you can link with your domain anchor name or use simple anchor as "click here" the fact is that the sites themselves are "infected". The infection can depend on a lot of factors, they are not 100% given. The charastestics can include: Were used as a pbn before. Links to casinos, pharma, gambling. Has hundreds of OBLs to shitty sites. Spammed links pointing to the site. Spammy anchor texts. etc. Be aware, read reviews and take precautions to not screw your sites that you care about.