Unit.prototype.sell = function () {
	if (this.type !== 4) { // Check if it's an item we want to buy
		throw new Error("sell: Must be used on items.");
	}

	if (!getUIFlag(0xC)) { // Check if it's an item belonging to a NPC
		throw new Error("sell: Must be used in a show window.");
	}

	var i, tick,
		sold = false;

	function ItemAction(gid, mode, code, global) {
		if (mode === 101) {
			sold = true;
		}
	}

	addEventListener("itemaction", ItemAction);

	for (i = 0; i < 3; i += 1) {
		this.shop(1);

		tick = getTickCount();

		while (getTickCount() - tick < 1000) {
			if (sold) {
				break;
			}

			delay(10);
		}
	}

	removeEventListener("itemaction", ItemAction);

	return sold;
}