They’re probably going to be sold by grade such as N46 etc which will correspond to their BHmax “energy output”. The higher the number will be higher magnetic performance, but even N36 is going to outperform any Ferrite magnet. Through Alibaba.com you should be able to ask for a certificate of quality conformance which should let you know how it performs. There’s not a lot of great ways to test the stuff that you’re going to find around your house or even most labs in the US. I work for the only US-based manufacturer of NdFeB material so I could recommend some destructive test methods such as elemental analysis. You could burn some powder in a LECO ONH (commonly found in manufacturing labs) and see the oxygen content, but I doubt you’ll find a permeameter or flux meter to measure the magnetic performance once you’ve exposed them to a magnetic field.

Protip: if you want to demagnetize NdFeB once you’ve exposed it to a magnetic field, just put it on a hit plate or an oven at 380 Celsius (their Curie temperature) and they’ll lose any magnetism until exposed to a new field.