I sold a brand new sealed Poco X3 phone on eBay that I didn't want, I stated no returns as it is too much hassle. After 4 weeks, the buyer claimed they had kept it as a present and had not opened the phone and there was something wrong with it, I asked them to contact Xiaomi as it was under warranty. They refused and demanded a refund, eBay naturally sided with the fraudster,.
I am getting the phone back a month later today.
I suspect they have tampered with the software, how would I check this?