I tested my indoor sensor (Davis Airlink) by comparing to others in my neighborhood -- I set it up outside on the first bad air quality day we had and an hour later it was with 5 AQI points of the 4 PurpleAir sensors within a quarter mile.

Certainly not professional level calibration, but shows that it's within the ballpark. Unfortunately I don't think there's an official EPA monitoring station within 10 miles so I can't really check it against a calibrated monitor.

Aside from trying to buy a commonly used reliable device, that what the match test was for. When my device was reading 12ppm pm2.5 and a blown out match made it read in the 100s clearly the device is working to some degree of accuracy. I could've checked it outside I guess but I think local air conditions would predominate over any official city average I could have compared it against.