Everything so far has been about your own site. Off-page SEO is about signals from elsewhere — principally links from other sites, which have been a core part of how search engines assess pages since the beginning.
A link from one site to another is a kind of vote. Search engines treat it as evidence that someone thought a page was worth pointing at — and because links come from independent parties, they are harder to fake than anything on your own page.
Not all links weigh the same. A link from a well-established, relevant site carries substantially more than one from an unknown site with no relationship to your subject. A hundred links from low-quality directories are worth less than one from a respected publication in your field.
Every one of these has the same shape: give someone a reason to link, then make it easy. Nothing on the list is a trick, and nothing on it is fast.
Search engine guidelines are explicit that links intended to manipulate rankings are a violation. The main categories:
The consequences range from the links simply being ignored, through algorithmic devaluation, to a manual penalty against the site. The risk is real, and it is asymmetric: the upside is a temporary boost, the downside can take a long time to recover from.
Paying for a link is not automatically a violation — what matters is disclosure. A paid or sponsored link should be marked so search engines know not to treat it as an editorial endorsement:
<!-- Paid or sponsored placement -->
<a href="https://example.com" rel="sponsored">Partner site</a>
<!-- User-submitted content: comments, forum posts -->
<a href="https://example.com" rel="ugc">A link someone posted</a>
<!-- Generic: do not pass ranking credit -->
<a href="https://example.com" rel="nofollow">Some link</a>Marked correctly, a paid link is a legitimate advertising arrangement. Unmarked, it is the violation.
Link building is the slowest and least controllable part of SEO, which is precisely why so many shortcuts are sold for it. For most small sites, the honest sequence is: get the on-page and technical work right first, because it is entirely within your control, then earn links gradually by being worth linking to.
A site with excellent content and few links will usually outperform a site with poor content and purchased links over any meaningful timeframe — and it will not be carrying a risk that surfaces later.