You could try a variant of this (give someone a d10 and a d6, hide roll from surveyor, if the d6 comes up 1 they give you a 1-10 rating based on the d10 and are otherwise honest) but this may not be useful in cases where people aren't deliberately lying to you, and is probably only worth it if you have enough sample size to wipe out random anomalies and can afford to throw out a sixth of your data.

Or weight the die.