A Niche Edit Link is basically when the vendor edits the content on an existing page to include your anchor link. They can add a small sentence or para about your related content in context with the pages overall content or they can just add in your anchor to an exiting sentence etc. I prefer getting a few sentences added so the content that surrounds my backlinks is highly relevant to my topic to which I am linking out to – so the link juice is maximised Under all circumstances, never swap out a link… that is never change an existing link to your site link. This is core blackout link manipulation and Google also is pretty strict when it seems this happening.
You should look out for Niche Edit Links (or link edits) on fiverr also. These are also powerful – but use them sparingly and make sure the page you buy your link edit on has backlinks and/or traffic to it.
You can also do outreach for niche edit links fairly easily and get a high success rate by offering $$ to the guest post site owner. Its little work for them and they get to make quick money.