If this was going to be a daily working machine that was facing employees and life on an open trailer.... I'd say get over it.
In your situation..... you have a strong argument for getting a machine with cardboard dust still on it.
If your mower is destined for a cushy life of residential use and garage storage... there is no sense in starting out with a unit exposed to environmental wear.
I hope the dealer was'nt trying to pull one over on you.