we got our kitchen from hummelküchen (a bit north of Hamburg) and achieved a saving of 3% discount between the offer price and the selling price. the prices had already been negotiated by the construction company we built with. the electrical appliances were approximately at internet price. the difference was more than worth the installation, delivery, warranty through one company, etc.
the electrical appliances make up the largest cost item within the affordable/normal kitchen price range. the cabinets are anyway made of chipboard, the fronts then add another price element. and last but not least the countertop, which is either given for free (chipboard) or breaks every kitchen price (elaborate granite shape made from one piece and such things).
in the end, we were satisfied that our construction company "prescribed" the kitchen installer. one could also have gotten the value back (removing the trade), which according to neighbors was not really worthwhile. we went there 3 times until we signed everything including extras. everything else was clarified by the kitchen studio with our construction manager including delivery and assembly, etc... everything went smoothly and perfectly according to the construction company's schedule. also the on-site measuring before installation was done in our presence or similar.
I found that overall very good. however, the assembly guys were not so great. but that is another matter.