Exchanger reserve
The amount of currency an exchanger has available for a given direction right now. If the reserve is smaller than your amount, the exchange won't go through or will take time.
In more detail
The reserve shows how much the exchanger can actually pay out for a direction right now. If it is smaller than your amount, the deal will not go through, or you will have to split it and wait for a top-up. Choose an office whose reserve noticeably exceeds your amount: it is both a safety margin and a sign of serious volume.
