The serial# is right on the side of the machine. Weird not to give it to you. The Nolting Company is great and make wonderful hardworking machines. I own a pro 24 w/ 12' table. I would contact Noting and see what used machines they have right now. It is a big investment and the company will back the machine up and take good care of you.
I would suggest the old adage If it sounds to good to be true and if in doubt. If the seller seems reluctant to answer questions.......
I don't like the idea of cash either.
Hope you find a machine to love.
peace