There are two places to buy websites online
People can buy fake click to manipulate the Google Analytic Data.
Look for website that have commercial values.
Understand the value of the website you are going to buy (How?).
Higher the earning from the site higher the selling price.
Find websites that have potential to generate traffic.
If you can find website with quality content but less traffic due to lack of SEO, then you can buy that website.
Do the batch analysis with Ahref.
Check the DR of the website ( Filter out illegal and not interested website)
Check out the link profile of the selected domain. See the backlinks are related to the niche