1. The meter shows HOURS OF USE, not MILES. Two hours is roughly half a day's use for a commercial mower.
2. 2 hours of use on this mower is about 1/10th of one percent of its useful life span. That works out to about $5 of depreciation on the unit.
3. You said you drove the mower yourself. Do you think they just toss the mowers out after someone's tested one? Of course not. So obviously you know that they eventually sell those units. You both could have been more clear about which exact mower you were buying, and if it were a big deal for you to buy a crated model, you could have simply said so to make it clear.
4. The slight rust and paint flaws on a slightly used mower when you first get it are meaningless to its value down the line. I've got 8 y/o mowers that get daily use and don't have any rust that affects them functionally. So I wouldn't get in a lather about it.
It's one thing if they brought over a unit with a lot of hours on it and it was all banged up. They probably just assumed it didn't really matter much. Or, they thought they could dump an older unit on an inexperienced buyer and put a newer model on the floor. But either way, not that big a deal, and again, you should have made it clear you didn't want the unit you tested if you absolutely didn't want it. It may well have factored into the price you were given.
You may have poisoned your relationship with this dealer. It probably won't matter, since this machine should be well past its warranty period before giving any problems.
That's another thing. A unit that has been used a little will have the bugs worked out of it. A newly uncrated and set up unit may well have something that needs an adjustment almost right away.