One common problem affecting dishwashers is dishes emerging from the final cycle while wet or dirty. Other problems include: food gathering around the filter, a cloudy film (or spots or smears) on glassware, rusted cutlery, faded on plate patterns and foaming from the machine.
If dishes are loaded in such a way that water can run off rather than collecting in cups, bowls and other dishes and the user adds a drying finish to the load, but the dishes still come out wet, the heating element may be at fault. Touching the outside of the dishwasher during the drying cycle to see if the machine is hot is a simple way to test it.
When dishes do not clean, the issue may have to do with sort and loading or with the amount of detergent. Powdered detergent that has become damp in storage loses its cleaning power, and inexpensive detergents do not always clean as well. When food collects near the filter, it is time to take out the filter and clean it. Scraping off larger pieces of food from the dishes before putting them into the dishwasher is a good way to keep the filter clean longer.
A cloudy film on glassware suggests limescale deposits. Using an additive along with dishwasher detergent fights this. In areas with hard local water, the rinse aid setting may need adjustment. Streaking on the glasses may be surface corrosion, which is avoidable with a lower temperature cycle. Rusted cutlery may be of a lower grade of stainless steel or may have stayed in contact with acidic or salty foods such as ketchup or mustard. A foaming machine can mean that too much hand dish soap stayed on the dishes when they went into the dishwasher, or the rinse aid chamber might have a leak.