One of the Appsumo deals I signed up for was, absolutely, a scam.
My advice would be to only sign up for these offers if you won't be upset if some of the vendors refuse to honor the text of their offer, just assume that some will pull a bait-and-switch and you won't be too disappointed.
Do not think that you'll be able to persuade them to honor the offer as described, I made that mistake and simply wasted a lot of time; they know that, ultimately, no-one is going to bother taking legal action, so, they'll just stonewall you until you go away.
Also, pay extremely close attention to the expiration dates.
