Welcome to the forum. I split your question of into its own thread.
From an installer viewpoint, a % of the price is a % of the price. Plus ceramic is usually more difficult to install, so why not pay him/her that few bucks more?
From an owner viewpoint, you want to keep your costs as low as possible, and that upsell is some nice gravy.
If you are happy with your installer (and that's rare) it might be in your interest to cut him/her in on the upgrade IMHO.