Never extend a booking deadline!
Looking down the chain
You can avoid the deadline issue altogether if you structure your quote with two prices, one by a given date, and the other by a second date. The price difference can be quite motivating if the client knows the cost difference up front. Down the chain, some hotels will quote you accordingly, assuming you are not blocking too many rooms. If none of the above fits the situation, then you have manage the risks and evaluate deposits.