Hard water can be an issue
I had a friend with a higher end dishwasher (sorry, I cannot remember the brand at the moment but it was a "domestic" unit) but it was not washing well at all. Turns out the water softener had either been out of salt or malfunctioning for a while so the pump screen was almost plugged with mineral deposits and most of the holes in the wash arms were also plugged with minerals that had flaked off. She was using the cycles that added additional heat to the water, causing more of the minerals to precipitate out. I was able to clean 90% of it out with multiple rounds of Lemi-shine at several times the recommended concentration. :-O
30 grain per gallon hard water makes a big mess of things very quickly!
I have a 20 year-old Maytag DW, middle of the line, that still works perfectly and looks almost new inside. Unfortunately the racks are starting to rust out and it's not worth replacing them due to cost. But it has had soft water plus an iron filter all of it's life.