how to know these links good or bad quality!
yup, more like a public blog network lolIt's hard to say and authority metrics of the domain are easy to fake so when you check the metrics, go a bit further and give a look to the kind of backlinks the domain has. Is just another security layer.
Then just look at the the website. Nowadays people use marketing softwares to get data about a websits, but unfortunatly they don't look anymore at the website itself. Getting a look at the posted articles, do they have all outgoing links? Make some old school simple search queries like site:example.com and have a look at how is indexed respected to the number of pages the website has. Get a look of Google cache and the dates of last cache to understand how often Googlebot is crawling it.
Remember if you can buy a backlink there, someone else can do it, that means the private blog network is not so private. Does what I m saying make sense ?
buying from a seller here I would recommend asking for a list of the domains before buying linkswhat if a pbn has a 22% psam score or 40% and a seller here is selling them