welcome
i have using hundreds of DFPlayer until now, only a few have defects from fabrication such as short circuited and not properly soldered. it is very useful.
if your DFplayer is inside a case, then you can add USB B socket (to connect it to PC) or USB A socket (to insert a U-disk) so you dont have to open the case.
one more thing: check the main IC. if it has 24 pins, it is ok. if it has only 16 pins, the UART feature is not working