Geeze, you got it all wrong!
"If" I was buying it, I would tell them that the cab is just in the way and aren't buying it for the cab and consider that a liability, that way they sell it to you for less.... You do know that they are dangerous and are a rollover candidate which could trap you inside...
"If" I was selling it, then it is worth everything of that $3,500.00 and go from there... The fact that the cab will prevent the weather from affecting you or getting slapped by branches on trails...
You work from the side you are on, as the Buyer (talk down item) or Seller (talk up item).
As a buyer, you act as if you don't need it and the seller wants to sell it even worse and will discount it... IF the buyer is wetting his pants when he is looking at it, the seller knows he has the buyer by the short hairs and keeps the price high...
As a note, it looks like this Mule is at an equipment yard, so they have marked it up thirty to fifty percent or better when they took it in on trade for something. So you have room to make an offer, if they say five bucks, start at three...etc. The economy isn't that great for toys, so they don't want to sit on it very long either... also point out that it is missing a winch too, they may put one on for you to boot...
Also, the hour meter has to be broken or replaced, you don't wear out your front tires with that little "Low hour" wear since new. I would bet that the unit has a lot more time on it than what you are being told. Look for other items of wear points and point them out like they were poison to the deal. These guys, if they sell equipment are well aware the unit has a lot more time on it that what they are claiming... They are suppose to be the "Professionals"
Good luck!