I think he is using URL shorteners or custom URLs that looks like a blog but are a redirect to an affiliate URL. Now they'd have to start examining the URLs in detail, which is a lot harder. Especially if he cloaks for access that looks to be coming from Pinterest themselves.

If I were tasked with detecting these, nothing would run from a Pinterest IP address. Use throwaway VPS hosts on different blocks and replace them regularly.

For that matter if I were tasked with posting this spam, I'd do the same...