If your dishwasher isn’t working as well as you would like, that doesn’t necessarily mean it needs service or that it’s a clunker. Maybe you just need to perform some cleaning and/or maintenance. Have I already answered your problem in a previous post?
Or, if you try all of those and you’re still not satisfied, maybe you’re not using it correctly (see HOW TO: load your dishwasher properly) or maybe it’s time for a new dishwasher. How long have you had yours versus how long is a dishwasher expected to last?