Start with the same specification
Two prices are difficult to compare if the doors, windows or hardware differ. Ask for the manufacturer, model, dimensions, finish and glazing in each written proposal. Mark optional items separately.
Ask what installation includes
Review removal, disposal, track, opener compatibility and any finishing work. Clarify who handles approvals if they apply to your property. A short description such as “new door installed” can leave important items unclear.
Keep product and service terms together
Save the final specification, written warranty terms and the service contact. Confirm the schedule and payment stages directly. The most useful quote is the one whose scope you understand.