What a great question! Thank you for asking! Examples of things that may be considered to be a manufacturing defect include trolley handles that won't work at all, obvious, improper sewing that significantly affects the bag's function and/or aesthetics, an obvious, large mark/stain on the fabric, top bars that are missing the hinges, hardware (nuts/bolts, etc.) that has not been installed properly, zippers that are missing pulls.
Things that are not considered to be manufacturing defects include bending of the side supports of the bag (they're intentionally semi-flexible, as the bag is a soft-sided duffel after all), the materials used in manufacturing are intentional and by default not a manufacturing defect (for example, if a frame that supports a wheel breaks, it is due to some sort of impact or other external cause - the material cannot and does not spontaneously become broken on its own), drooping or loose extensions on the garment-hanging bar (there's a FAQ about this specific topic!), and tiny flaws in the fabric (we don't warrant or represent that our bags will be 100% cosmetically flawless).
We take a detailed look at each situation, case-by-case, so if you have anything about which you are concerned, we want to hear about it, with photos and/or video that clearly demonstrates your cause of concern. Even if it's not covered by the warranty, we'll have a solution!