This we know. And they work so well because it’s extremely worth it for an SEO provider to keep the website in good shape. Feeding it a bit of content once a month – and having 15 people paying $40/month for a backlink per website he owns means he doesn’t even need to rank websites. And you’re getting clean, quality backlinks – so everyone is happy, right?
Everyone is happy until you realize you’ve created a bit of a hostage situation between your backlink provider and your properties. If your website reaches X monthly revenue, you’ll be paying Y month in costs just to maintain your revenue. And if you wish to expand? Your costs go up again – significantly, to maintain your new ranking keyword positions.