  Using an example of the Abell 2634 galaxy cluster we discuss the effect of
contamination of kinematic data by interlopers and its impact on mass
modelling. The cluster data reveal rich substructure along the line of sight.
We demonstrate that it is necessary to apply a few independent methods of
interloper removal in order to obtain a reliable sample of cluster members. We
present results of three such methods which are commonly used in the literature
and have been recently extensively tested on simulated data. Only two of them
lead to consistent and reliable samples of cluster galaxies. For both of them
we provide parameters of the best-fitting NFW density profile by fitting an
isotropic solution of the Jeans equation to the velocity dispersion profiles.
