What Google says
Google’s spam policies define link spam as creating links primarily to manipulate rankings. The examples include buying or selling links for ranking purposes, exchanging goods or services for links, and using automated programs or services to create links.
Devaluation vs manual action
Search systems can ignore or devalue links algorithmically, and Google can also issue manual actions for spam. A third party cannot guarantee which outcome will occur for a particular link or site.
Paid links can have legitimate uses
Google states that buying and selling links for advertising or sponsorship is part of the web economy. It says such links should be qualified with rel="nofollow" or rel="sponsored" so they do not pass ranking credit.
Why PBN marketing needs scrutiny
A provider may describe network quality controls, hosting diversity, or clean domain histories. Those factors can matter for quality, but they do not override the purpose-based language in Google’s policies.
Practical takeaway
Use policy documents as the baseline, avoid guarantees, and distinguish between buying exposure/sponsorship and buying ranking credit.
Important policy context
Google's current spam policies identify buying or selling links for ranking purposes as link spam. Google also says paid advertising or sponsorship links can be legitimate when appropriately qualified with rel="nofollow" or rel="sponsored". Read Google's spam policies.