  We estimate the amplitude of the source-lens clustering bias and of the
intrinsic-alignment bias of weak lensing estimators of the two-point and
three-point convergence and cosmic-shear correlation functions. We use a linear
galaxy bias model for the galaxy-density correlations, as well as a linear
intrinsic-alignment model. For the three-point and four-point density
correlations, we use analytical or semi-analytical models, based on a
hierarchical ansatz or a combination of one-loop perturbation theory with a
halo model. For two-point statistics, we find that the source-lens clustering
bias is typically several orders of magnitude below the weak lensing signal,
except when we correlate a very low-redshift galaxy ($z_2 \la 0.05$) with a
higher redshift galaxy ($z_1 \ga 0.5$), where it can reach $10\%$ of the signal
for the shear. For three-point statistics, the source-lens clustering bias is
typically of order $10\%$ of the signal, as soon as the three galaxy source
redshifts are not identical. The intrinsic-alignment bias is typically about
$10\%$ of the signal for both two-point and three-point statistics. Thus, both
source-lens clustering bias and intrinsic-alignment bias must be taken into
account for three-point estimators aiming at a better than $10\%$ accuracy.
