Don't fret. It's their job. They own a store and are probably used to bending over backwards to help customers out. This was nice of them, it's not like you or Home Depot had a gun to their heads. They sold an AC, more than likely got paid to deliver it, and got a very nice tip from you. If stuff like this were able to ruin their day they wouldn't have made it to the point of managing their own store. So don't cry over it. At least they have jobs and each other. I think it sounds kind of nice, actually.
*without even looking up from work*
Callisto, from Xena: Warrior Princess. Why?
I'm the person inviting you to the comedy shows and if you ever actually came to one I would seriously be so amazed at your awesomeness I would be willing to help you move and possibly even consider us best friends.