As a cabinet rep, I deal with quite a few issues relating to warranty items on cabinets after they are installed. Some issues are problems with the cabinets themselves and some are related to the installation. This is especially true when dealing with frameless cabinetry. One of the main issues is that sometimes the homeowners have installed the cabinetry themselves or have hired their own installers so the last thing they want to hear is that it is an installation issue.
When the issue is a warped door, It's easy to check the door and see if it is truly warped or if it is actually an issue with how the cabinet was installed. Simply remove the door from the cabinet, and remove the handle from the door. Lay the door face down on a flat surface (a granite counter top works great for this). push down on one of the corners of the door and see if is bounces. If it bounces considerably, then the door is warped and should be replaced. If it bounces slightly, this can usually be addressed with the hinge adjustment on the cabinet. Obviously if it doesn't bounce at all then the door is fine and either the hinge needs to be adjusted or the cabinet is twisted which is an installation issue.
The cool thing about doing this in front of the customer is that they can plainly see what you are doing. It doesn't seem like you are trying to blame the installer or "Pass the buck". You are there at the home trying to help the customer and get to the bottom of the real issue.
If the door is warped, simply replace it and everyone is happy. If the door is fine, you can do your best to adjust the hinge and if that doesn't work, you need to get the installer involved.
If you're thinking "I'm not sure how to remove the door or how to adjust the hinge" that's great! that means there is a need for the video that I'm working on for my website. I'm going to try and have it up by next week. this will show how to remove the doors with the most common hinges used today (Blum) and how to easily adjust them. If you as a kitchen designer know how to remove a door and how to easily adjust the hinges, you seem knowledgeable about the cabinets that you sell and that makes you more valuable to your clients and the referrals that will come from them!
Thanks for reading!