They may not want to deal with the hassle of taking it somewhere else. Sure there would be no issues you bringing someone to look at it at their place as long as nothing is being taken apart. If there was then I would be hesitant to buy.
If the health benefits or the thousands of dollars they spend on smoking a year won't motivate them to quit do you really think a few extra days off will?
So he made you an offer and you accepted then you did not keep your acceptance and wasted his time? Sounds like he wasn't the jerk there. All you had to do was say no.
You mentioned no batteries? Does that mean you will need to run the Genny all night for the furnace? I would throw in at least one batt to run lights and furnace at night time.