Always Agree on the Price
Not negotiating the price before agreeing for a service. Back in Thailand a taxi driver offered to take me with his motorbike around the city. Sounded fun and the chap looked ok so I agreed. When I asked how much it will be he told me not to worry about it, he’ll make you good price for me. I don’t remember exactly how much I ended up paying but it was a lot.
Lesson learned: Always, always agree on the price first.
Story credit: Reddit / leviathaan