if you contact AMD they will send you a cpu to put in so you can update the BIOS for the new Ryzen chip. no reason to think it won't work with any other compatible cpu.
not sure why the shop is trying to scare you, but this is exactly how you are supposed to update that BIOS. there is always a small risk but if they know how to do it, there is little chance for a problem.
i would be questioning them heavily if they are scared to update a BIOS themselves. that's enough for me to go elsewhere for help. i personally would not even hesitate to do it, nor bother suggesting there was some risk involved that i would not be responsible for. it should be a simple thing for a "professional" shop to do.