They aren't going to an exchange due to slippage.
So you think that your liquidity is high enough to beat the exchange price even with your "premium"?
Such large trades that they will get a better deal at your premium as opposed to the slippage they would encounter at an exchange on top of spot rate?
How much premium % are you talking?
I would like to know so I can go calculate how much BTC would have to be traded with a market order in one slam to make your premium the better deal, because slippage..