My Samsung ML-2850D printer is connected via USB to an Airport Express. I print to it from my Mac over WiFi. I want to check how much toner is left, so I know if I need to purchase a new cartridge soon. However, when I check the Supply Levels via system preferences, it says "Information Not Available." What is the best way to reliably find out how much toner is left?
Attaching a printer using Airport does not provide the same capabilities as attaching through USB, and one of the things that will not work is querying the printer for paper/ink levels etc.
When you have the printer attached locally, the driver has the ability to talk over USB for lots of things, including these services, reading from a card reader that may be on the printer etc. Once the printer is made wireless, these facilities are lost, and it effectively just becomes a dumb queue that you can drop a print into. About the only feedback it can give is if the printer is offline or not. If your printer is multifunction, you'll likewise lose the scanning/fax stuff also.
So unfortunately the only way is to hit up the printer direct, walk on over there and take a peek.