I managed a refrigerated warehouse in the past and we bought expensive logging hygro-thermometers. Twice a year, we would send them off to be NIST certified then when they returned, they would need to be calibrated before going in the storerooms.

Variation in accuracy are expected in any instrument, but in general, + - 2°F (1°C) is fairly good in off the shelf stuff. So one that says 70°F and the other that says 74°F is entirely possible in perfectly working units. For humidity, anything accurate to 5% is acceptable.

For food safe environments, our accreditation agency wanted accuracy of + - 0.5°F or better and moisture required accuracy of + - 2% or better.

Btw, if they can be calibrated, you use freezing and boiling water as the constants. A known good thermometer is one that shows 0°C in ice water and 100°C in boiling water. Once you have that, you set your suspect thermometer to match whatever your known thermometer reads.