I'd take the SN off of the tractor and call kubota corporate and see if this unit has been sold before. Kubota does not do 0% financing on used equipment....not that I've heard of anyway.
For one to be a stand-up dealer, they'd have to be honest. Pulling a fast one and substituting a used machine in place of a used one.....well there is nothing but dishonesty there. I'd report the incident to kubota as well and see if they have had a history of these types of transactions.
As per the tach hours on the machines.....I think you'll find just about all of the tractors use them. If you have a digital display you may be confusing a timer option and actual machine hours. Easiest way to test it to look at the hr meter before the next warm-up session; watch the hr meter to tick over to the next 10th hr which should take between 0 and 6 minutes, and then time how long it takes for the next 10th to go by. If it's longer than 6 minutes, your machine is counting revolutions of the engine and not seconds that it's running. Actual revolutions is a far more accurate way to ascertain use than a hobbs meter.