Has anybody else ever had people show up to your convention games expecting to be playing a completely different game based on a sloppy reading of the description?
I had a group expecting Apocalypse World because I used the word Apocalypse in the scenario name even though the game description was clearly something else.
I had someone expecting 5 Torches Deep come to a game of Torchbearer.
There was another time that GURPS Transhuman Space got mixed up with Eclipse Phase.
These sessions were by far the worst convention games I've ever been in. The players quickly disengaged, dicked about, fell asleep or left the game when it wasn't what they thought it was.
How can a GM stop this from happening? Or if it does what can you do if this is clearly happening at your table?
It happens. What helps is to put the name of the system and setting in all relevant and prominent spots. Title, First line of description, last line of description. Summary, all tables or bullet points. It's pretty much the only relevant info and it should be unmissable. Then keep the rest of the test super short. The more text you have the less people will even read one sentence. They are going through all the convention games looking for one or two to join. They won't read more then 3 to 5 sentences. So you don't need more.
That way this shouldn't happen a lot. If it still happens occasionally I'll usually tell them, hey we are playing Blades in the Dark not Age of Darkness. It's a game about heists with flashbacks. Wanna join in anyways?
If yes cool. Of not then cool. We start with the rest. For convention games I'm always prepared for complete newbies to the system or even TTRPGs in general. So it doesn't matter if they come in blind.