You don't. You don't need to interact with any websites to make transactions. It's on-chain. You can always run a (light, non-archival) node to ensure the transaction does exactly what you expect it to (before submitting it) do without ever going to a website.
You're right that if you trust absolutely nobody, not even chain explorers, you need to put in more work, do some digging and understand how the system works. You're exchanging usability for security/trust. The point is that you have the option to do that. If you are paranoid and don't trust centralized entities you don't have to. Decentralized exchanges can't cheat you, steal from you, freeze your coins, or go under. It's technically impossible because they don't have custody of your coins at all.