DA is what I stopped caring about, because it's a useless Ahref's metric.
DA is Moz. DR is Ahrefs. Not picking on you, half the industry swaps them daily, but it's worth keeping straight because the two fail in completely different ways.
DR is pure link graph. Nothing else goes into it. That's why a weekend and a pile of expired domains moves it, and why it's the easiest number in this industry to inflate on purpose. DA is Moz trying to predict ranking ability, so it's a guess about an outcome rather than a count of links. Gameable too, just slower and with more moving parts. Retiring both is fine. Retiring them for the wrong reason means you'll fall for whatever replaces them.
always important to check whether the site actually ranks in Google before buying a link
Right instinct, and it's the test I'd keep if I could only keep one. Tighten it though, because "does it rank" fakes as easily as DR does if you never say ranks for what.
Every PBN on earth ranks #1 for its own domain name and its own invented brand. Type the name in, sea of green, site looks alive. Means nothing. You're the only thing competing for that string.
The version that survives contact: does it rank for terms it doesn't own. Non-brand, commercial, something with real competition in the SERP. Then look at where the traffic actually lands. If the only wins are its own name, its tagline, and a handful of zero-volume long-tails nobody types, that's a site that ranks for being itself -> nobody is linking to that on purpose, so why would your link there count for anything.