"I'll just go to FedEX" Okay, have fun

Had a customer today trying to get something professionally packed and shipped and then paid for by their customer because they didn't want to be responsible for anything. Despite it being their sale, and them specifically saying they wanted it professionally packed (so ofc they have to pay for that service), they wouldn't accept that we can't take someone's card over the phone if the cost is over $80, and they said "Okay then I'll just go to FedEX." I simply responded, "Okay, it's up to you. We have packing experts here, and if you'd like, you can pay here then have your customer pay you back. If not and you you want to go somewhere else, we can't stop you."

Dunno why these customers think that threatening to go somewhere else will change anything. I'd never say it, but I would honestly much rather they go bring their crabbiness there than having their argumentative behavior holding up a line with customers who won't give us any problems