Your goal is to make the buyer a more educated consumer, so that he/she will recognize reality and adjust expectations to meet reality. If the buyer is unable or unwilling to do so, then have a talk with the buyer. Explain that you're unable to provide what he/she is looking for [actually, what he/she is looking for doesn't exist] and suggest that the buyer might be happier with a different agent.
Work out a referral agreement with someone else in your company, and suggest that--among the people the buyer might wish to interview--is the person with whom you have a referral arrangement. Suggest multiple people, though. And it's probably appropriate/ethical to disclose the referral arrangement. At least you might make something if the buyer ever buys. But you have to take into consideration your own time . . . which will continue to be wasted if the buyer won't recognize reality.
Discuss this with your broker, as well. He/she may have some other suggestions.
Hope that helps.
Are you in a counter offer stage? if the seller has issued a counter offer but the buyer does not agree, then ask the buyer issue his own counter offer to keep the ball rolling. If the buyer doesn't do anything, then technically, the deal is dead. There is no obligation on either part.
And as Bill said, and there are more of us who will say the same thing... 'NEXT!"
Almost always, these types of head-butting situations have to do with a difference in communication styles. So, perhaps you've been telling them, well, that doesn't make sense, the sellers aren't going to come down that much, et cetera. Maybe instead, just hand them listings of pending sales in their price range. "I just thought you'd like to know what's been selling recently!" Let them figure it out on their own!
Or, the other 'way round. Point being, sometimes we keep talking to them in the same way, waiting for different responses. If we change things around a little, maybe they'll respond differently!
All the best,