It does have some teeth. Disney v Redbox ended up ruling that Redbox could not resell digital copies of movies from bundle packs because Disney had in the terms

It does have some teeth. Disney v Redbox ended up ruling that Redbox could not resell digital copies of movies from bundle packs because Disney had in the terms that it was only allowed to be sold together. But there is another case that went all the way to the supreme Court regarding resale of textbooks. Kurtsang v wiley. Textbook publisher Wileyclaimed that because they put "not for sale in the US" on their cheaper, but nearly identical international version textbooks, that meant they could dictate as such. But the defendants prevailed and the supreme Court ruled that the first sale doctrine applied and lawful purchasers of the books could import them and sell them wherever they want. This is a rather recent precedent because Costco lost a similar case v Omega a few years earlier, but it did not set a precedent. The textbook one did. But I suspect that there were some additional copyright and licensing complexities that made the Disney case different. Especially since it was two copies of the same item, just in different formats. Also, Disney, so probably the most experienced, well funded, and vicious gang of lawyers in existence. But I'm not sure if a straightforward resale of a digital item has been tested in the courts. It seems with the Kurtsang v Wiley precedent, you would have a good chance of winning.