Great ASSumption.
I consider the world a fine place that everyone else, other than you, is not you.
Have you not ever ridden other's rig before?
Clarification for SweetLou:
I would do a few miles to demonstrate to an intersted party the nuances--handling, shifts, flex, etc.--of the used rig (my rig, that I ride, tune, and otherwise keep in what I consider adequate riding condition).
Then a quick refit to the intersted party's ergo's, and I even get the pleasure of evaluating another's rig, as well as a short ride with another cyclist. I consider it a most polite way to treat another cyclist.
Oh, wait....
You rode away in a huff--or in whatever state-of-mind which caused you to hop on your bike and ride away.
Bummer for me.
.
Ok, I'm the ass because you are not clear. You did not say that you rode your bike, with the buyer along on their bike, then switch. You never mentioned that the buyer would have a chance to ride the bike. The only thing you said was that you rode your bike and the seller would ride whatever they rode to your place. I did not assume anything. I just took your words as fact. I did not assume you switched, because you didn't say that you did.
The OP asked about what to do with buyers wanting a test ride. Your (incomplete) answer was that you rode your bike. Nothing about the two of you riding together as you go over the bike, then allowing the buyer to ride it to see the characteristics that you have pointed out.
So, I asked you some questions about how that process worked. Then gave my opinion of how I thought your method was silly. Because I just couldn't imagine watching someone else do a test ride for me, especially the seller. But for some reason or another, you didn't like my response. But instead of expanding on your response to make your process more clear, you decided to imply that I'm an ass and the world is a fine place because everyone else is not me. I find that quite insulting.
Now, if I was the buyer and you said that you will ride along on the bike that is for sale, then switch. I would agree to these terms. As long as I could ride the bike. But you didn't say that.