Arrange for a test play of all instruments before recommending them or refusing them. You need them at least a week. Contact schools who already use the brand in question. The manufacturer should have a list of references. Next, whoever you buy them from should provide free maintenance for at least a year. And the manufacturer should offer a manufacturers warranty. The longer the warranty, the more confidence and pride the manufacturer has in their product. Make sure parts are available.
Most reputable brands say their instruments have a 10 to 15 year lifespan in a public school situation. Things happen and all will need to go to the shop at some point. Many repair shops that are attached to retail stores will not repair something if they donít have a source for parts (a good independent shop can make many parts). Even if they can get the parts they still may not repair something they donít sell so look for them to talk the instrument brand down regardless of how good you think it is. Find another store.
Finally, donít forget to go back and test new versions of the ďacceptedĒ brands with the same scrutiny...you may be surprised.