Yes, I have said no. I was actually delivering birds. They were going to free range them and did not have an adequate pen to home them to. I technically did not have to say no as I explained to them what they needed and they understood.
Normally, if they come to the farm, I sell them what they want. I cannot police everyone. I have had a few instances where I felt, but did not know for sure, that they were not going to be the best caretakers. I make it clear that the birds are as is and once they leave the property they are theirs. I also hand out a sheet that has basic care and worming instructions. I also offer to orally worm them at the time of sale. I emphasize that putting a bird in a new location exposes them to new and different worms/parasites and that a regular worming regimen is very important.