Hello Hans,
some internal matters and terms regarding the customs in the construction business:
S&R appears to be a pure specialist dealer with a showroom. The tiler has one contract with them; they also send customers for selection and behind the scenes their surfaces and parts list for your project. Then everything is delivered to the construction site on account, exactly on schedule, with appropriate logistics and in the correct quantity. In other words, the tiler has minimal effort with logistics and can focus on his core business, the laying. You will then receive the cost estimate from the tiler.
Negotiating with the specialist dealer is normally not possible. These are often the manufacturer's list prices. Self-supplied goods are, however, reluctantly processed by tilers due to logistics, incorrect quantities, warranty, and quality. Smaller one-man businesses sometimes do this upon request. The bigger they are, the less likely it is.
Often the specialist dealer offers a discount scale for the tiler depending on the quantity sold, meaning he receives a commission at the end of the year depending on sales volume, also for the goods you bought. If at all, you can try to negotiate the discount here, maybe he will play along. Given the current situation in construction, this is rather doubtful. Haggling with the specialist dealer is out of the question.
And: the specialist dealers usually carry all the major manufacturers. So it doesn't really matter which one you go to. The size of the showroom itself is naturally different. Therefore, feel free to visit another showroom (even if the tiler does not work with them), maybe you will like a tile there that you didn’t find at the first exhibitor. Then ask the first one if they can also order it for you. That’s how we, for example, got our bathroom tiles.
PS: my brother runs a tiling business.