The advice saying pay cash on collection should be qualified, in as much, as you will have no protection from eBay if you subsequently have problems.
The only time I’ve received negative feedback on eBay is when I sold an ebike. The buyer met me at my address, took it for a test ride and then paid cash for the agreed amount. 24 days later the buyer contacted me claiming that I had been dishonest about the state of the battery as it needed replacing. I certainly hadn’t been dishonest. The buyer wanted a full refund and complained to eBay. eBay were not interested in helping the buyer as they considered that the sale had been conducted outside of their platform, ie cash was paid.
Just as an off topic point. I sold the used ebike in good faith. The battery seemed fine when I sold it. I made it very clear in the advert that the battery wasn’t new. Had the buyer contacted me within, say, a week of collection and informed me that the battery was knackered, I would have considered contributing in part or whole to a new battery. The fact the buyer waited 24 days and very aggressively claimed that I had deliberately miss sold the item, they ended up with nothing.