Let's consider this XKCD comic from a while back.
And we have a marketing dilemma. It is entirely possible to make your business proposal sound too good to be true.Â Reality tends to punish people who accept these offers, hence the part where things sound too good to be true.
If you find yourself temped to promote a business idea and people are telling you that it sounds too good to be true consider doing just what the character in this comic did and keep the car. If your idea is so incredible maybe just keep it for yourself. If it actually works you'll probably be richer and have annoyed less people.