I’ve had similar experiences of people being really offended even though you’ve clearly laid out terms.
I had a pair of pa speakers to sell a few years back. A guy contacted me and said he’d pay by a certain day so I put them on hold. That day came and he didn’t pay. He gave me some sob story about the money he was expecting not arriving in time and it would instead be arriving 2 days later. I gave him the benefit of the doubt and told him that the money had to be in my PayPal account by 6.00pm on said day, otherwise I would take them off hold. He agreed.
Of course the money never arrived, so I took them off hold and promptly sold them to the next in line. What followed was an absolute torrent of email abuse from the guy. Even though he fully understood what I said I was going to do, he saw it as a huge injustice and called me everything from a pig to a dog.
Hey ho, you live and learn.