A quick way to sanity-check whether an exchange booth is “good” is to look at how tight the buy and sell rates are. The smaller the spread, the less you’re paying in hidden cost.

Example right now at Superrich (green) HQ for a $100 bill: 3,154 THB buy vs 3,162 THB sell — a spread of 8 THB, i.e. ~$0.25 (about 0.25%). If you assume the “fair” rate is roughly the midpoint, your effective cost is about half the spread, ~0.125%. That’s a bargain.

Not to mention there are other advantages to using cash.

Just keep in mind rates vary by company and by branch (besides time of day / market moves, of course). Both Superrich companies have websites showing their current rates.