How does he know it's pee? Did he open it and take a taste? It could be a severely overestimated lemonade party.
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See, this is where these people are dumb. You tell them you'll take the money up front, in cash, something like $500, or you'll make them look bad. Then they pay you, and you take the money, and when they return with recording gear, you tell them to fuck off, keep the money, and enjoy the rest of your evening knowing you grifted a scumbag.
Keep it.