Sorry, you can't be our customer
There are interactions marketers have with prospects where the prospect wants something and the marketer or organization just isn't interested in delivering it. These interactions almost always end badly.
I visited a Blockbuster store in London, hoping to rent an appropriately Royal-family focused DVD. After a bit of search, I found it. Would they sell it to me? No, it's rental only. Oh, can I rent it? (I asked with my full US accent). Sure, fill out this form.
Five minutes later, they said, "Oh, you're from the US. You can't rent here." What about if I pay as much money as it would cost if the DVD got lost? Nope. What if my hotel vouches for me? No.
Here's the thing: From the rational consumer's point of view, this is silly. They should take my money and we'll both be happy. From Blockbuster management's point of view, though, allowing clerks to start making up exceptions and prices is just too much trouble. And it probably is.
You can't (and shouldn't) please every single person who may or may not become a customer. But you should (and you must) figure out what to tell the folks you're going to turn away. Endless negotiations are like teaching a cat to swim... the cat never learns and you get frustrated.
"I'm sorry, I appreciate your interest, but you can't be our customer. We can't please everyone and we're focused on customers with different needs just now. Can I suggest you try the place down the street? I'll draw you a map."
The power of this outcome is that you have the freedom to figure out exactly what someone has to do in order to be a customer. You can qualify people by asking the right questions. You can take no for an answer.
If it turns out that you're getting too many 'no' responses, too many people walking out empty handed, it's probably time to reconsider what you need from someone in order for them to do business with you.