What is the appropriate method to clean non-transferable wall stains unacceptable to shippers?

The appropriate method to clean non-transferable wall stains that are considered unacceptable to shippers is power grind/paint. This method is effective because it not only addresses persistent or ingrained stains that may not be removable through surface cleaning, but it also prepares the container for repainting, ensuring that it meets shipping standards.

Using power grinding can effectively remove the stained area while allowing for a new layer of paint to be applied, restoring the container's appearance and protecting it against further damage. This method is particularly useful for areas where stains have penetrated deeply or have become part of the container's surface.

Additionally, while scraping might work on surface stains, it may not address deeper marks and could potentially damage the container's wall if not done carefully. Hot high-pressure washing can remove some types of stains but may not be effective for non-transferable stains and could even cause water damage to any seals or joints. Spot clean, although useful for minor blemishes, may not have the same thorough impact as power grinding when dealing with stubborn stains. Thus, power grind/paint stands out as the most appropriate method in this scenario.