When I have purchased them the seller's always say "it does not work". But they only have ~50 balls for the machine.
They need a few hundred to make them work. Inside they have a hopper for the payout. If the hopper is not full the machine won't let you launch any balls. It would be like a slot machine without any money to give a payout and that would make the customers very angry, so it won't let you play until it gets filled up.
Buy ~500 balls online, they are cheap. Fill up the top hopper and you maybe surprised that your machine works just fine. Once you start to fill the top hopper up you will see things start to move and understand what I am talking about.
The only thing I had to do on one was flip it around and hit it a few times with it at different angles to get some balls loose that got stuck in a weird spot and bound things up. The machines are not made to be kept at any angle other than straight up, but they end up getting stored at weird angles and balls end up in bizarre locations that they would ordinarily not be able to get into.
They are neat and I would encourage people to pick one up if they see one for sale. $100 is the top price in my mind for a nice one with a few hundred balls.