I agree with Freetochat, go along armed with your readies but check the machine as best as you can before you hand any money over.
As i said before i find it a bit strange that even though he has a showroom he does not take credit cards, but even so i would take one along with you and ask him if he will take one in the showroom, because if he does you are covered by your credit card company if anything goes wrong.
He may not take them on ebay because most of the time any buyers might live the other end of the country, and they cannot complain to their credit card company if they did not use it.
I maybe way of base here and he might be a stand up guy, but his email has made us think that something is wrong.
I hope everything goes well.
Woody