Promoting SEO services on FB and G ads, worth it?

Is it worth it to promote SEO services (such as PBN links, guest posts and stuff) through FB and G ads? How is the ROI ? I guess it is permissible there, or is it banned niche ?
I want to sell directly the backlinks and stuff, not all round SEO service (doing all the work to move the site in SERPS).
Pls anynone with experience in this niche, waiting for your thoguhts...

still relevant