At that point what do you do? If I had been able to pick up on time I would have had the pick of the litter. A nuc is a functional hive in every aspect except size. Just like the best beeks in the world will have some weak hives and some good hives and some really strong hives, the same is true for nucs. When making nucs up we estimate what we will have available to sell... once you collect someones money you really can't call them up and tell them that you can't give them what they ordered.
In the ideal world money would not be collected until the customer picked up the order, but that isn't always possible and frequently if you want bees you have to pay ahead.
The other issue for new beeks is often they are unwilling to actually inspect a nuc and even if they did, they would not know what they are looking at. They are just so happy to have a box with bees it in that they would not even see the flaws with their particular box.