The heritage/cooked flour frosting is another alternative that is less sweet. All frostings have their advantages or disadvantages though. Some need to be fridged, others don't, some smooth nicely, others don't, some are greasy, others aren't etc. What your customer might want, and what you are willing to make, are sometimes completely different things, and it's ok to say no to people. I do it all the time - you either like my frosting, or you don't, but I ain't changing it.