I probably should add that it can get even hairier than what we've covered so far. Suppose I shoot a picture of Alan with no model release (I'd never do that, even with a model release) and put it in a gallery. The picture sells. The buyer then uses the picture in an advertisement for his marihuana business. Can Alan sue the new owner of his picture? Can he sue me?
Typically the photographer is not the one who is being sued, it is the end user, so you would be free and clear. Even if you were sued, more then likely the gallery (assuming they know what they are doing) would inform the buyer that the purchase of the print does not authorize him to use the image commercially and the gallery may even require the buyer to indemnify the photographer to cover such cases. This would allow you to then sue the buyer for not only breach of contract and copyright (their commercial usage), but to also settle your other court costs with the other case.
More then likely though, you would not even be brought into the suit.
However, the business owner would certainly loose in this situation.
This actually happens in contests all the time. Usually what happens is some clothing company is looking for a lot of free images and runs a photo contest with some (usually worthless) prize to the winner, like a $500 gift certificate. Of course buried in the contest contract is pretty much a rights transfer clause that states you are allowing them to use your images however they want. They then use your images, but the person whom is in the images never signed a waiver for the company to use the images. That person then sues and wins a large amount of money, or that is how it use to be. Nowadays, companies that do this also add another indemnification clause in the same contest contract stating that the photographer has a model release for all people in the image and, if not, they indemnify the clothing company from any lawsuits.
This is why if you talk to any pros, they are leery about enter contest nowadays.
Building supply manufacturers do this shit all the time. Typically I get a request from an architect asking me to sign a release for some contest they want to enter my images in and I then have to explain to them why I can not sign due to the rights grab of the contest and a blanketed indemnification clause. Many understand, but it is always an uncomfortable conversation to have.