The Teslameter FM 302 can be tested before purchasing.
You get a new teslameter and probe with up-to-date calibration, including certificate.
The trial fee is on a weekly base. If you decide to purchase, the trial fee of the first week is droped.
We offer all of our series teslameters on a trial bais.
Optional Linearity Curve
Optional you can get a linearity curve for the probes.
Examples of these curves, see here: 
data sheet AS-active-probes and here Application Note PE003 Linearity Curves.
Notice to Trial Based Teslameters
Test devices are currently only available in Germany.