“Dofollow” is informal shorthand
There is no rel="dofollow" attribute. People commonly use “dofollow” to mean a regular link without nofollow or sponsored qualification.
Sponsored
Google says rel="sponsored" is the preferred way to mark links that are advertisements or paid placements. nofollow remains acceptable.
Nofollow
rel="nofollow" tells Google not to associate your site with, or crawl the linked page from, that link in the normal way. Google treats these attributes as hints for crawling and ranking systems.
Why buyers should care
If a service sells a placement specifically on the premise that payment will buy ranking credit, understand that Google's spam policy explicitly addresses that practice.
Primary references
Primary references