Start with the spec sheet and the box, not the showroom floor. Put the two sheets side by side and read the same lines in the same order.
Check the rack first. Count the tines on the lower rack and see whether the upper rack folds or lifts. The label lists a rated place-setting capacity, but your cabinet and your habits decide the rest. Measure your largest pot and your tallest glass, then test them against each rack in the printed diagram.
Next, read the cycle list. Note which cycles include a heavy soil option, a quick wash, and a sanitize setting. Ask which cycle the unit uses as its default, and how long that default runs. A longer cycle that cleans well on the first pass may suit your week better than a short one you have to repeat.
Then find the sound rating. Ratings are measured under a stated test method. Compare only ratings that cite the same method, and ask the seller to show you where that method is printed. If the two sheets name different methods, the numbers do not line up, and the comparison is not fair yet.
Finally, check access to the parts you will touch most. Find the filter, the spray arm, and the door gasket in the manual. Ask which of those a homeowner can clean or swap without a tool, and where replacement parts are sold. A unit with easy filter access is easier to keep working.
Write four lines on one sheet: rack fit, default cycle time, sound method, and filter access. If either side leaves a line blank, ask before you decide. For the upkeep side of this choice, see the dishwasher service life and planning page.