Buy tiles cheaper somewhere else?

Better not. He towed like a pro, the rest was rather so-so. In that respect, I wouldn't overestimate this factor ;-)

No, it is not irrelevant. How is the dealer supposed to know at what price the construction company sells you the tiles? If you build by individual contract, you might also go to a showroom of a wholesaler or a middleman. They show you tiles and can tell you what the normal sales price, so to speak the RRP, is. But whether your tiler gives you a discount and if so, how much, the dealer doesn’t know either. It shouldn’t be different for you. I am still missing the answer to the question of whether you have even discussed the surcharge with the construction company... so it sounds like you haven’t. If not, the discussion is pointless. Ask your construction company what surcharge they charge for the tiles, everything else is nonsense. You are speculating here about a hypothetical surcharge.

No, here moisture meets "it was done like this in the past". For functionality, it is actually better not to tile the entire wall height. Tiles cannot absorb moisture. That is why most people only tile the shower wall up to the full height or to a certain extent. Everything else only as high as necessary (splash water/cleaning).

I have different information. Floor-to-ceiling tiles are more hygienic, prevent mold and many other things. Yes, some things in the past were not worse. Quite the opposite.

I have different information. Floor-to-ceiling is more hygienic, prevents mold and many other things. Yes, some things in the past were not worse. Quite the opposite.