I understand the whole issue of asking if someone is buying the car alone, or would have to consult with a partner. I've had work in my life where I got all excited over a deal... only to have the wife call me back and say their husband isn't happy with whatever the arrangement might have been. And here I'm only talking about $200, not a $20,000 purchase.

A car is a lot of work, both physically in showing the person the car and paperwork-wise. Its a necessary and very valid question. Perhaps to cut down on the condescending edge to it, you might say "now I hate asking this question, but the dealership requires I ask.... would this purchase be something you are soley responsible for, or do you have a partner that needs to have an opinion?" Hoe can a person take offense to that? Its honest and takes the edge off before you ask. They know that you're uncomfortable asking, therefore making them more comfortable with you, they realize you know the question could be insulting and you are considerate of their feelings.