  We study how well halo properties of galaxy clusters, like mass and
concentration, are recovered using lensing data. In order to generate a large
sample of systems at different redshifts we use the code MOKA. We measure halo
mass and concentration using weak lensing data alone (WL), fitting to an NFW
profile the reduced tangential shear profile, or by combining weak and strong
lensing data, by adding information about the size of the Einstein radius
(WL+SL). For different redshifts, we measure the mass and the concentration
biases and find that these are mainly caused by the random orientation of the
halo ellipsoid with respect to the line-of-sight. Since our simulations account
for the presence of a bright central galaxy, we perform mass and concentration
measurements using a generalized NFW profile which allows for a free inner
slope. This reduces both the mass and the concentration biases. We discuss how
the mass function and the concentration mass relation change when using WL and
WL+SL estimates. We investigate how selection effects impact the measured
concentration-mass relation showing that strong lens clusters may have a
concentration 20-30% higher than the average, at fixed mass, considering also
the particular case of strong lensing selected samples of relaxed clusters.
Finally, we notice that selecting a sample of relaxed galaxy clusters, as is
done in some cluster surveys, explain the concentration-mass relation biases.
