Sites like Fiverr will sell you some quick and dirty services for onsite keywords and link building, however, they normally lead to heartache and penalties from Google. You can absolutely get 100k backlinks from these less than reputable seller on one of these sites, but a by-product of this is that they send out a script that posts to a low-value wiki, or blog comment systems. It is usually not too damaging and they will send you a reporting spreadsheet with all these wonderful links.
Sometimes, these links will cease to exist long before Google can index them which means you threw money away and got nothing for it. That can often be better than the alternative, which is when the links exist for months, Google finally index’s them and then starts to penalize the site because the sites associated with it are spammy or contain malware.
Contributors: Simon Ponder from Image Freedom