Even though the temptation to leave with both the gp and the cash would've been high, I would've probably (at least, I like to think I would've. Would ofc be in a completely different state of mind in the actual situation) let him have the GP after beating him up and just let that serve as a lesson. Really depends on the other person. Don't know why he wanted to meet in person and use cash for the transaction if he was planning to scam lol, but I won't get into that here. Anyway, you could have probably handled the situation in a much better manner, but I don't judge you. I would've done the same. I'm always up for giving a beating for someone who needs it, otherwise kid will never learn.