We test all of our PCBs thoroughly before they are shipped. We do ship the PCBs bare though, which means they are susceptible to ESD and other damage. We really can't warranty against how different people may handle the PCBs.
We publish handling instructions that are also shipped with the PCBs, found here
An issue many run into with Flight Core is that they plug USB into the Spektrum port and fry the board.
The RMA diagnostic process is for ModalAI technicians to spend time looking into the root cause of the failure, and then provide analysis on what to do next.