Cash is legal tender for debts; "This note is legal tender for all debts, public and private." You don't have a debt just because you're standing in the office talking to them, so they don't have to accept cash as payment or impose other legal restrictions. They could perfectly well require payment in lima beans or monopoly money or western union money orders if they wanted, though that might not be good for business. By the same token, you're free to leave without conducting any business if you don't like the terms, as you did.
If you had stayed for the night first and had to pay on the way out, you would then owe a debt, and they would have to accept cash payment (or I suppose forgive the debt if they preferred). In this hypothetical situation, of course, they may also accept payment in forms other than cash if it's mutually agreeable.
