I don’t expect to get the current exchange rate when paying in USD cash on the island. Merchants/restaurants aren’t in the currency exchange business. If they accept USD cash then they’re doing me a favor, and there’s a cost (to me) associated with that. I carry USD, Euros, and plastic, and I pay with whichever is most advantageous to me. That’s usually a credit card with no Foreign Exchange fee.
I haven’t used the Currency Exchange on the island in years. Exchanging cash there will likely be done at a premium, but at a more favorable premium than at the Foreign Exchange kiosks found in US airports.