I kind of against people DIY install dishwasher and garage door opener if you are not very professional. First it is not too expensive to for a professional install, you only save about 80 dollar if DIY. Second if your installation is not done right could cause secondary demage. In case of dishwasher for most new townhouse with a finished basement if there is a leak you may demage the drywall in basement. In order to find the leak and repair you may have to open up ceiling. It costs a lot.
In case of garage opener there are small adjustments needed to done in order to avoid overloading the motor and gear. If these jobs are not done right, the opener wouldn't last very long.
I recommand people use installation service from the place they buy the stuff. You only can test machine after you install it. If you install it yourself, when there is a problem they can blame you for installation error case the demage.