Domain Rating (DR) and Domain Authority (DA)

This is the most consequential misunderstanding in the field. Both scores are proprietary models built from each vendor's own crawl of the web, and both are logarithmic — moving from 20 to 30 is far easier than moving from 70 to 80. Because the vendors crawl different portions of the web with different methods, the same site routinely scores differently in each tool, and neither number is wrong; they are simply different estimates.

The scores are still useful, in the specific way an estimate is useful: as a fast, comparative filter when you are looking at hundreds of candidate sites and need to triage. They are a poor basis for a hard threshold, because a site's score says nothing about whether its audience overlaps yours — and topical relevance is the thing that actually makes a link valuable.

Filtering purely on these scores also has a predictable failure mode: it selects for sites that have optimized their own score, which correlates uncomfortably well with sites that sell links. A high number with no real audience is a warning sign, not a qualification.