I think it is perfectly reasonable to outline your expectations before hand. Much better than expecting to be able to spend hours going over the unit only to find they have 5 others they are delivering and won't be able to leave it connected but for an hour. All they can say is that it doesn't work for them and then you have to make the choice to buy there or not based on their answer. But as was said, whatever you do, get it in writing in the official paperwork.
When we were looking, we went to a couple of dealers who had camping sites on-site at the dealership and encouraged you to stay the first night there specifically so you had plenty of time to try everything and make sure you understood it and it worked. If something needed attention, they would take it in first thing the next morning.