I never buy links and this is a good approach IMO. If you want to purchase, purchase a few but links from qualitative sites.
And number of ways, If a competitor sends in a complaint, if they go to the site and it says $99. for a link. I'm sure they have also have some formulas also that can red flag sites to be checked on.
the most simple formula example: if the website about music linking to manufacture, casino and seo websites Google will certainly understand that those links are bought and will check this website as SELLING LINKS
I voted, but actually I think that there are free ways to promote websites even in very competitive niches.