There is no set standard for when this happens. Keep in mind the buyer will be skeptical of you saying no payment was received, so keep an open line of communication with him, preferably by telephone. A few questions to ask are whether the payment is trackable when cashed? Is the delivery of the payment trackable? Was it sent to the correct address? Without payment in hand, I would not send anything. However, if the payment was really sent the two of you should work together to figure out where it went.