So it is always smarter to reflash your used Asic miners when you buy them? 🤔🤔🤔🤔, wow I don't know this, I got two Asic miners used from China and I don't see or notice any strange things happening, I connected to Nicehash pool and get paid as per what the calculator showed, I will be more careful next time.
If one just updates the Firmware to the latest I believe this means the older user is not using any unknown or separate Firmware.
Sometimes they do get a very small hashrate from your miner just like other firmware with a developer's fee of around 2% to 10% without you notice.
That is why if you buy a used miner it is always recommended to flash them through an SD card and then upgrade it to the latest firmware to make sure you are using clean firmware. Dev fees don't affect much if you only have one miner but for those who have big farms, a 2 to 10% dev fee is a big loss.