If they are not receptive to this suggestion we will design their work to the best of our ability. We know what is hot and what is not, and that's good enough for most people. We've built enough kitchens and media centers so that most people trust our judgment. I would like to add another word of advice on designers. Direct your customer towards professional designers who are familiar with the type of project that you're working on.
Designers are like every other trade.
They range from great to incompetent. Some specialize, and some try to cover everything. Like woodworkers, some know their limitations and some don't. Sit down with the customer and ask them if there is a layout that they prefer. You can put sinks in front of the window as it is done traditionally or they can have something different like a sink in the island or corner.