What to look for when buying links


I'm considering buying links for one of my sites as I think it must be possible to buy links that work:)

However, before I do it I would like to know if anyone of you have experience with it and know what to look for?

Things such as moz score, different link profiles, age of site etc.

I searched for buying links and I only got three hits. Please link to other resources if I have overlooked some.