I listed something for sale by auction. 

Someone asked "can I check it to see if it's compatible with what I've got?" Of course, come and see it tomorrow. 

Ebay deletes the message and removed the listing!

I and the potential buyer work out that they have to buy it first. Ok, I'll relist it. No I can't relist it because I tried to sell it outside Ebay!

No I didn't, I'm actually trying to sell it THROUGH Ebay! I have to create a new listing just for them, they have to buy it (and Ebay takes their money), before they can come and test it. As it happened, it wasn't suitable, so I now had to trigger a refund (which costs me money). 

I wasn't trying to sell outside Ebay, but Ebay seem to be trying to make me since I can't sell it with Ebay because they won't let me! And why do I have to pay to refund?

Even at a boot sale or jumble people can look at the stuff and sometimes even turn it on to test it. 

"To make buying on eBay a safe and enjoyable experience" - huh! To make it a complete pain in the rear for both parties, more like.