Bit of an embarrassing admission, but for the first year or so I was buying crypto I never checked the rate beforehand. I would just pick an amount in my local currency, tap through the purchase, and accept whatever BTC figure came back at the end. It never occurred to me to verify any of it. Then a friend asked me how much I had actually paid per coin across a few purchases and I had no idea. I could not reconstruct it from memory and the exchange did not make it easy either. Since then I have started checking the rate before I commit, which sounds obvious in hindsight but apparently was not obvious to me at the time.