The North American Woodwork Standards (NAAWS) classifies cabinet installation into three levels of quality:
Level 1 - Economy: This level of quality is considered to be the minimum standard for cabinet installation. Cabinets at this level may have slight variations in level, plumb, and square, with gaps between cabinet parts and with hardware not being perfectly aligned. Level 1 installation is considered acceptable for lower-end cabinetry and for projects with a tight budget.
Level 2 - Custom: This level of quality is considered to be above the minimum standard and is usually what is typically installed in the residential housing market. Cabinets at this level will have minimal variations in level, plumb, and square and gaps between cabinet parts, and hardware will be properly aligned. Level 2 installation is considered good for most residential projects.
Level 3 - Premium: This level of quality is considered to be the highest standard for cabinet installation. Cabinets at this level will have no variations in level, plumb, and square, with no gaps between cabinet parts, and with hardware being perfectly aligned. Level 3 installation is considered excellent and it's usually requested for higher-end or custom cabinetry, or for commercial projects where quality is of the utmost importance.
It's worth noting that while NAAWS is a widely recognized standard, but it's not mandatory, and some manufacturers may have different levels of quality or they may have their own specific standards, that vary from NAAWS. It's important to be familiar with the manufacturer's guidelines and have a clear understanding of the level of quality that is expected for a specific project.