Someone wants ear buds, they want to signal wealth so choose expensive brand, but they want knockoffs because they're actually poor[er].
The main risk with knock-offs is they arrive broken, or just don't arrive, or... basically it's a scam of some sort.
So, you took on the risk of buying, assessed the earphones as working, the earphones are now probably worth more as they've been QC-ed (by you), moreover the buyer can actually see them working and refuse them if they wish.
Within the context the buyer seems relatively rational.