In more detail
A link is written as <a href="https://example.com" rel="sponsored">. Google's guide to qualifying outbound links describes three values:
- rel="sponsored": for links that are adverts, paid placements, sponsorships or affiliate links
- rel="ugc": for links in user-generated content, such as comments and forum posts
- rel="nofollow": for other cases where you don't want to imply endorsement or pass ranking credit
Values can be combined, for example rel="ugc nofollow". Since 2019, Google has treated all three as hints rather than strict instructions. It may use them to understand links better, and in some cases may choose to crawl or consider a link anyway.
There's no "dofollow" attribute. The term is informal shorthand for a normal link without these values.
Marking paid links correctly matters. Google's spam policies treat buying or selling links that pass ranking credit as link spam. Sponsored placements are acceptable when the link is qualified with sponsored or nofollow.
Why it matters when hiring an agency
If an agency arranges paid placements, sponsorships or advertorials for you, those links should carry rel="sponsored" or rel="nofollow". An agency that promises paid links will be "dofollow" is selling exactly what Google defines as link spam.
Nofollow links still have value: they can bring real visitors, and mentions on respected sites support brand awareness. A natural backlink profile includes a mix. Be wary of agencies that dismiss every nofollow link as worthless, or count only followed links as proof of success.