Is this a viable business model for connecting people together?
It can be. But it's more likely to get scammed.
I see you changed your original post. There are enough exchanges out there that have a
high market volume. If you seriously want to sell a large amount of Bitcoins, contact some of the reputable exchanges. If you provide them a signed message proving funds, they might be able to help you out. I know a Dutch exchange manually handles requests above the default maximum limits.
