Locals: shop around for the place that sells it at the lowest cost. Take extra time to go to different stores for different products even if they’re all available in one place. Regular price too high? Vote with your wallet and don’t buy it. Good price but you don’t have much money? Buy less.
Wealthy foreigner: This is cheap. I’ll take it.
No one needs to know your income. The price may be the same for everyone, but if you’re willing to pay a higher price, then they’ll be more likely to keep the higher price, thus reducing everyone else’s buying power. If you buy more than the locals and help eat up their stock, that again incentivises keeping prices where they are, or even increasing them. The storekeepers don’t care about how much money you have. They look at whether things sell or not, then make their decisions based on that.