I send out checks all the time for our business. We tell anyone that hasn't received their check to allow at least 3 weeks for the delivery because we know it can easily take that long to some areas. If they don't want to wait that long, I have them pay the stop payment fee and I'll re-issue the check. If they wait that long and it hasn't cleared the bank, I'll pay the stop payment fee and re-issue it. In 20 years, I rarely have had to pay the fee.
We've had mail returned to us 6 months after it was sent out marked that it was caught in a machine and found during maintenance.
We've had other mail delivered to us in error and have had to put it back in the box to be delivered correctly...some people will just rudely toss it away (think that might be illegal in some way).
We get mail that has been ripped, torn in half and just plain nasty arrive in postal envelopes saying "something appears to have happened to your mail during delivery", well duh!
Bottom line, please allow more time as long as the seller is understanding also.