What is this backlinks service?

In researching one of my competitors, I found numerous websites which all serves one purpose: to give backlinks to others. Here is one such optics-online*co*uk (this is not mine, and I am not advertising it).

Links are under adverts, and they are obviously indexed.

What I want to know is: What kind of service is this and where can I use/buy this service? I cannot find any JS or PHP or some script behind it, and it is hard to believe that somebody is doing this manually because I found several hundreds sites so there must be thousands.

Any help is apreciated. If this question is in wrong place, please move it :)

check the ads here, they talk by themselves and are bh confirmed I think, most of them at least.

please delete my post