These are couple of things I check when selecting backlink sites for SEO purposes. I found this list of things to be most useful and actually make a difference with backlink sites.
Does the site exist in a niche or category similar to your site?
This is the first and foremost thing to check. If the site you are trying to get a backlink from is not relevant to your site or your business, then that backlink might not be that helpful for your sites SEO. Backlinks from similar sites or sites in the same categories add more relevance and weightage.
Did you already acquire a link from that site?
Sometimes you might have already gotten a link from that backlink site. It’s good to keep track of all your backlinks so that you can quickly check if you’ve already gotten a link from that site, so that you don’t put your efforts in the wrong place. This can be done by keeping a list of all the backlinks you acquired on a Google Sheet, Notion database or an Airtable.
How much traffic does the site get?
This can be checked through SEO tools like Ahrefs, Semrush, etc. One thing to remember is that, the SEO tools often show low traffic numbers compared to the actual traffic the site might be getting. The benchmark for the amount of traffic a site needs to have varies depending on the niche and what kind of quality of site you are looking to acquire a backlink from. People seem to have different opinions regarding whats the minimum number to consider here, but for me, I try to look for sites which have a minimum of 2500 unique visitors per month on average over the past six months, when checked using Ahrefs or Semrush.
Anchors & Outbound links
Check for any weird or potentially harmful anchors and outbound links. Things like adult text in anchors pointing to the site or adult websites, casino, gambling, etc websites that the site might be linking out to should be checked as well. These things hurt the quality of the site and getting a link from such site might affect you as well.
Redirects
Check if there are any high amount of redirects for page URLs. Sometimes site owners purchase expired domains and redirect those expired domain pages to the new site to give it a boost. This might help the backlink site have a higher authority, but this affects the site in the long term when all those link redirects eventually become insignificant. Check carefully for these kind of things. You can look at anchors pointing to the backlink site to see which URL they are poiting to and see if there are any large amount of redirects.
Backlinks vs Outbound links
Check the difference between backlinks and outbound links. This shows how many backlinks the site is getting and how many backlinks the site is giving out. If there are more number of backlinks than outbound links, that means the site is receiving more backlinks than it’s giving out, which is good. But if there are more outbound links and the difference between backlinks and outbound links is huge, then that site is probably being used as a link farm, and its best avoid those kind of sites.
Authority score (Domain rating / Domain authority)
This is sort of a superficial metric made up by the SEO tool companies. At one point I think this used to have some importance, but now this doesn’t need to be given priority (in my opinion). I look for a minimum authority score of around 30 for a backlink site, if it’s a little bit below that, I still don’t mind. Traffic, outbound links and overall content are much more important compared to this.
Overall site content
This should be given the highest priority. If the content on the site reads too much like it’s written by an AI bot, then that’s not something readers would be interested in going through. Read some articles published on that site and see if that’s something a reader might find useful or interesting. This is something basic that people often ignore, but unless someone actual reads something on that site, that link you want to get wouldn’t be much useful otherwise.