Hi, pony, welcome to the forum. I have several really great meal and bar shops I do each month with one of my kids. That is probably what you are referencing. The requirement is for 2 people to eat and one orders an alcoholic beverage to see if the bartender/server checks that person's ID. The person ordering the drink must be 21 (legal drinking age). Most clients require that IDs be check on all patrons who appear to be less than 30 or 35. The point of the shop is not to trick the client into doing something illegal but to document that by not checking, they could potentially do something illegal. That way, the client has NOT done anything illegal by serving the alcohol, but the server who did not check ID before serving has violated the company's policy and will be censured, up to and including termination.
For example, One client I have shopped is a restaurant/bar chain. The requirement is that you are a mystery shopper until you finish eating, after which you ask for the manager and reveal yourself to him, giving him signed paperwork, and you tell him whether the server passed or failed. At this chain, if the server fails, the corporate office requires that the manager fire the server immediately for policy violation. I liked this shop as long as they all passed. Then one day one failed and both the manager and the server started to cry. Yes, literally, both men cried. Immediately terminated. It wasn't fun anymore. That was my last one for this chain.