Oh man, that's the worst (and way too familiar). Fell for a similar one in Barcelona once where the "historical stop" was just a fancy olive oil store. For Prague, the Sandemans New Europe tours are usually legit, they work on tips so they actually try to make it good.

Wait, you're just taking some random guy at an airport coffee cart's word for it? That's a bold move. I would not expect a barista at a normal shop to have any clue what a "half-pour" is. You're basically speaking a secret language you made up.

Sounds like you dug your own money pit.