Curious, which country are you from?
In this case I would choose gpus that do not need to change BIOS for good results.
Im from Israel
No need to flash bios for mining (just if you want to squeeze last 0,x MH from it, in my opinion doesn't worth the risk), also if the card is dead, bios is useless. I don't think they desolder bios for checking it if was flashed or not, also if they do that, you can blame them for flashed intentionately that bios/or hardware modiification especially for voiding warranty. Is your word against they word. I don't know they are accreditate to desolder bios chip or make hardware modification (as seller or service, it they are not official AMD), any hardware modification will void automatically warranty. I think important is to have intact AMD sticker on screew.
flashing bios is not only for 0.xMH, there are many more reasons
and in my case, card was not completely dead, i was working but crashing all the time, so they could check the bios.
it is also my fault for not flashing back to original - i was young and stupid back then LOL