I had this problem, unwittingly, yesterday.
I was working a busy market selling my baby clothes and to entertain the customers kids I made a few simple models. It wasn't long before there was a small queue of kids waiting for balloons. The market was coming to an end, the wife was dealing with the last of the customers and it was time to get cleared up.
I gave the last half a dozen kids a balloon each and told them I had things to do, but, if they could bring the balloons back when they've blown them up I would make them a model. Not one of them came back, or if they did, I was long gone
