I have sales people and bean counters who are trying to sell customizations to clients, which is fine. But when a complex change request comes in that I send back a large estimate for, they get confused. Often they come back at me with "Why can't you just add another column?" which by another, they mean a dozen or so custom columns PER client.
So far all I can come back with is "We are trying to keep the database well normalized" which means nothing to them. I tell them I can create a system of tables that allows each client to define their own set of custom fields, but of course that takes more time and money than "just adding a few columns". And of course they want to have their cake and eat it too.
So how can I make them understand?
The best way I've found is to show how you can create a new feature out of what they're asking for that you couldn't add with just a couple customized columns. Features are better than customizations, especially when you can charge someone for it.
Try to make a good business case for your side before you get into the technical stuff.