A garage door opener is a small job on paper and a fitting problem in practice. Before you commit to a unit, go through the list below. Each item is something you can check yourself or ask an installer to confirm in writing.
Check the ceiling clearance
Measure the height from the highest point of the door's travel to the ceiling, and note the space from the door's top edge to the back wall. The opener's rail and the door hardware need room above the door when it is fully open. A low ceiling can change the rail style that fits, so confirm the clearance before you compare models.
Check the door balance
Lift the door by hand, slowly, with the opener disconnected. A door that is hard to lift, sticks, or drops quickly points to a spring or cable problem. An opener does not correct a balance problem, and a new unit working against a poorly balanced door will wear faster. Have the spring and cable checked before the new unit is set.
Check the outlet and the wiring
The opener needs a grounded outlet near the ceiling on the track side. Find out whether the outlet has the protection your local rules require, and whether an extension is needed to reach it. Do not run the opener from a cord across the garage floor.
Check the door type and the track
Sectional, one-piece, and swing-type doors take different hardware. Note which type you have, the track size, and any custom bracing. Give the installer the door's details in writing, so the unit they quote is built for the door you own.
Check the safety sensors and the reverse test
Confirm that the unit includes the photo-eye sensors and the auto-reverse feature. The sensors must be mounted at the height the manual specifies, and the reverse test should be done at installation, with a board or other object placed under the closing door. Ask the installer to show you the test before they leave.
Ask the installer these questions
Who mounts the unit and who runs the reverse test? Is the old opener removed, and who handles it? Who issues the warranty, how is it registered, and what does the document say is not covered? Get the answers in writing, and keep them with the model and serial record for the next planning review.
Compare the warranty before you sign
Read the warranty paper, not the summary. Look at the registration step and the exclusions, and check the published typical service life for the system on this site before you accept any statement about how long the unit will last.