OK so this subject has been brought up in some other threads.
I consider this to be a legitimate question. Maybe it would help for the customer to ask it in a different way. Most people don't think of better words than "do you have" or "can you make" a less sweet cake.
But anyway, there are lots of good European based recipes that ARE for less sweet cakes and icings and fillings. They have more eggs to do the work, and some use nuts instead of flour. The fillings are usually perishable, and probably not permitted by most cottage food regulations. That is a real problem for some bakers. But YES they can be decorated and stacked just fine.
Not every business will offer such cakes. The need for refrigeration is a limit for delivery not to mention outdoor venues. They take a little more skill to make, and they need to be sold at a premium price. But "making a less sweet cake" is a great way to build word of mouth for your business.
So if anybody wants to start looking for recipes, go borrow a copy of Julia Child's "Mastering the Art" from your public library. Follow the instructions for when to mix with a machine and when to mix by hand--this is critical for these less sweet cakes.