Hi - I’ve only sold one fairly cheap road bike (£250) via
eBay. The buyer came to collect and I offered to let him take it for a spin if he paid in full. We had an agreement that if he didn’t like the bike I’d give him his money back. As it happens he was happy with the bike & just paid and took it. Personally, I would always ask for cash upfront before letting anyone go for a ride. I think most reasonable people would understand your rationale, and I would question anyone who was reluctant to do so. Good luck with the sale!