In Venezuela, the price difference between the official dollar and the black market rate is a huge 24%, and this is an advantage that many use to their advantage, since businesses in Venezuela are required to charge the official dollar for their items.
I normally don't use cash. I always have BTC or USDT, and when it's time to pay for something, I exchange it for bolivars (at the black market rate) through an online exchange (100% reliable). This way, I always end up spending less or saving 24%.
Basically, if a product is marked at $10, I only have to exchange $7.6 and pay with bolivars.
It's incredible, but it's true.