I had a woman do this to me a few years back.
I had a hifi for sale, not a top of the line one but fully working.
I only wanted £30, she drove me mental to take £15, then £20, in the end we agreed on £25.
She turns up in a 3 door, tiny car, which is fine, except there was at least 7 people squashed in the car, and when DH took it out to her (after we offered to show her it working and she declined, saying she was in a rush) her boot was full up.
She told DH to put it on our drive and she would make room, she gave me the cash and we left her to it.
Then I heard an almighty bang. She had dropped it by trying to force it into the car.
I thought, here we go, she's going to want a refund. But she drove off instead.
About a day later, I got an angry message, using some rather inventive choice words. I had sold her a "shitter" that I was a "effing c**t" and she would "throw this shit through my window" if I didn't refund her £25, plus £20 for petrol and inconvenience. She then reminded me she and her associates knew where I lived.
Clearly she thought I would be frightened into paying up.
I messaged saying no chance, your car was a tip, you dropped it from the boot getting it in around various people and crap, and that after the transaction was completed its no longer anything to do with me.
I then said my opposite neighbour had the full incident captured on their CCTV, and should she like to threaten me or follow up on the threats, I would contact police and they'd probably be interested in the state of her vehicle and the fact 7 passengers were in a car designed for no more than 4.
The fact is, you don't know what happened after it left your property. So I would say, no, it left here in good condition. Then block.
People like that who try and manipulate for a refund are cheeky fuckers, hoping to get a freebie.
If you carry on selling, take full photos of the item