Most cabinet ware washers have square baskets of circa 350mm, 400mm or 500mm. Manufacturers specify how many glasses or plates will fit their particular machines, so make sure you buy the model that fits your operational needs.
Ware washers heat up a lot of water. Most utilise a 240v mains power supply. The lower the amperage the machine is, the longer it will take to heat water. So, when the machine is busy, sometimes it may only have a couple of minutes between washes to recover. Is a cheap 13amp machine enough for your business?
A gravity drain machine means when you pull out the drain plug, the water in the cabinet will drain away of its own accord. If the drain in your premises is above the level of the machine waste however, water isn't going to drain up hill, so you'll need either a stand to raise the level of the waste outlet, or an internal drain pump.
Wash cycle times are important. Make sure Glasswashers and Dishwashers have a dual timer fitted. Between 2 and 4 minutes is fine for both, but you'll also need a long-wash or continuous cycle on a Dishwasher.
Ware washers need 2 chemicals to do their job properly: detergent and rinse aid. That means that unless you have a wall-mounted, external chemical injection system, your machine will need 2 on-board chemical pumps. Check to make sure that they are included as standard.
If you buy online, be prepared to get your credit card out if your machine goes wrong. Online suppliers make a big thing of warranties, but once you've parted with your money beware, because many insist on an up-front payment when you claim. Some may think this is a rip-off, and in most cases, they'd be right.