Why buy links for your website?
When you want to have a good referencing on Google, there are several pillars on which you must play: content, technique and netlinking. Concerning the latter, the strategy consists of acquiring quality backlinks, i.e. from sites whose theme and semantics are related.
Indeed, if you sell bicycles, a link from a website selling cookies will not be very relevant in the eyes of Google! So once the reputation of the site has been checked, your website should then benefit from the 'link juice' or 'seo juice' and gain in reputation.