The dishwasher drain must be connected before the P-trap, not after it, which is what was done here. With this improper installation, sewer gases have the potential to come back in to the dishwasher.

Maybe you've never had a dishwasher and you're ready to give your kitchen an upgrade. Or maybe your current model just isn't doing the job you need. In any case, you know that getting a new dishwasher ...