Well, being willing to negotiate doesn't necessarily preclude giving them away to someone who seems particularly in need, with the agreement that they can pay him back in kind in the future.

He thinks over the offer - a process which is interrupted by a fit of stronger coughing. He can certainly make more potions, and the gold will buy local ingredients, if it turns out his potions aren't entirely effective in their base form.

And, of course, the man may well leave if he gets what he wants, and take that oppressive aura with him.

"At that price, seems the least I could do is test one out before the sale is finalized, to be sure the batch came out as intended. I wouldn't want to be smote for cheating a holy man, after all." The last is said with the most winsome smile he can muster.