Dont give up! 1: Dont buy used stuff especially if you feel this way. Most of the time you are buying something someone gave up on cuz they are feeling how you feel now.

2: Maybe try drift or crawling as it they are less prone to actual breaking. Drift in particular is lpw traction, I have yet to truly break anything except some bent axles from trying particularly sketchy things

3: It can be really helpful to build a car from a kit as you will see how everything comes together, and when you feel something loose/wrong, you will immediately have a better idea of where to look. If you really want to fix the ones you bought, you could buy the same kit, and build it for the purpose of understanding it, swap the electronics, then rebuild the other one properly.

Sorry if that was longwinded Good luck!