Trying to understand how the fee system works and why exchanging from fiat is much more expensive than exchanging crypto.

Ok, cryptocurrency exchange fees are usually very low because it costs little to nothing in fees to exchange them, unlike fiat itself. Banks charge a commission for everything, and there are many regulations and financial bodues to contend with who would ultimately want their own piece of the cake.

That might explain why there's a 0.25% fee when you exchange crypto on changelly, for example, and 7% fees when you want to exchange from fiat.
But at the same time, there are services with a much lower fee. BUT lower payment doesn't guarantee good quality service. And this is where I want to hear your opinion

Question #1 - how often do you buy crypto with fiat?
Question #2 - how do you choose the platform? Are there any other criterions than the amount of fee? Security, speed of transaction, simplicity, friendly service?
Aren't you afraid that your personal data may be stolen or sell somehow?