Using 3rd party parts cause Unsuccessful repair for iPhone?

There are certain repairs that cannot be done by third parties. TouchID, FaceID and certain critical IC's are all code-locked or paired to the logic board. Depending on the type of repair you want or need to do, this may or may not be an issue.

If you are mainly changing screens and doing modular repairs, then be wary about Home Buttons and now the ALS on the iPhone X. Apple is working hard to maintain full control over anything that is critical to the protection of user data. Every once and a while, a new update breaks something with cheap aftermarket parts. If you use only good quality parts and buy from a trusted vendor, you should be good.