...if I say "Buy my ebook or people will sit on your head and fart." I mean, obviously, I don't have an army of people spying on prospective customers to sit on them if they don't buy. The entire idea is absurd. Of course that won't happen. Nobody's going to chase you down and fart on your head if you don't buy my ebook. But would the FTC complain, or am I pretty much safe?
As funny as this idea sounds, I don't think you understand what the FTC does. They wouldn't give a shit about something like this. However a good lawyer would have a field day with it and bankrupt you.