Upload & Sell: Off
Three things to look for:
Electrical connections. These maintain the communication between the camera and the lens. Without them, you're gonna shoot everything in total Manual mode.
Mechanical connection. Somehow, the camera needs to let the aperture close when the image is taken. Lacking this connection means you need to stop the lens down manually before taking the shot (unless you like focusing with a stopped-down lens!). And many lenses today don't have an aperture ring, so stopping one down gets problematic.
Build quality. Cheap tubes will let the lens sag when two or three tubes are installed. They may also not be parallel between the front and back. Usually the cheap tubes use plastic mounts.... good ones use metal.