~ plenty of people with the technological know-how have already reviewed its code considering its popularity, meaning you don't necessarily have to review it yourself, and that you need to trust the developer less.
note that in most cases if you are downloading the binaries instead of the source code and compiling it yourself, you are still trusting the developer 100% because you are running a closed source application when you download the compiled version.
although there is a simple (to use but complicated to create) solution to this and i only know two wallets that do it, it is called "deterministic builds". bitcoin core and Electrum are the only wallets that i know of which do this. it means if you compile the code you will end up with the same binaries (eg. both have the same hash). so you could verify if for example the .exe that Electrum releases is the same thing as their source code or if it is different.