OK. You own the tricycle. You get to decide who plays with it.
But, I'm the customer, I get to decide who I give business to. As my grandfather used to say, 'All they have to sell is service.'
Frankly, If I were you, I wouldn't be so snippy to your customers, even ones who are snippy to you
.
Instead, how about letting us know why you can't do what appears to be a straightforward transaction for us. The Sotheby's numbers appear in the regular ebay auction search, so I don't understand why it's so hard. Let me guess, you think you should be charging a bigger commission on the kinds of things that Sotheby's usually sells? Fine. Go for it. I'll gladly pay a bigger commission.