I'll tell you how I do it, Perhaps it will help others. I split and sell 100 - 125 nucs, have now for several years. (mostly in 10 frame equipment) (some in 5 frame wooden nucs), I send an invoice, but collect no money until nucs are picked up. The invoice will tell the customer what to expect when they pick up the nucs. I give an estimated date they will be available. After the split and the installation of new queen, I wait until the queen has layed and new brood is capped. I then call (or e-mail) the next person on the list. No need to call if the nuc is not ready. If the customer confirms that they still want the nuc(s), I place their name on the nuc, and they can come and get it at their convenience. There is virtually nothing else I need to do to them once they are ready for pick up. As more nucs are ready, I call or e-mail the next names on the list. Everyone gets a good nuc, or I would not have called them to say they are ready.
To my knowledge, I have never had a nuc to swarm. There have been times that the five frame nuc in ten frame equipment will have 7, 8, 9 or even 10 frames filled by the time the customer picks them up. If a five frame nuc gets overcrowded, I may have to put it in a 10 framer, and give the customer another 5 frame nuc.
I have not had complaints, but, if I did I would want to make it right. If you don't, you won't be selling nucs very long. I close the entrance on nucs before daylight on the day the customer is coming for pick up, (in order to get all the bees) so the customer doesn't see the nuc until they get home, but, they have the invoice which tells them what to expect. Unless they know nothing about bees, they will be able to see if the nuc they receive, is what I told them to expect.
Of course things can go wrong after pick up, but, I don't feel I have ever been rooked by anyone. Of course I have replaced a few queens, over the years, for whatever reason did not perform as the customer thought they should. I have replaced a nuc or two in the past, but I have never had a customer that I could not work with, because I would want to work with them, even if it hurt me. Anything short of that and you risk getting a bad reputation.
This has worked for me, hope it may help others to see the supplier and customer side of the nuc business. Granted, I am a peanut size nuc supplier in relation to the big guys. But, your reputation is your greatest asset. You earn that, it is not given. If it is lost, it is difficult to get it back.