  We determine the efficacy of the kinematic Sunyaev-Zel'dovich signal
extraction pipeline, using pairwise kSZ measurements, in recovering unbiased
estimates of the signal and inference of the associated optical depth. We
consider the impact of cluster co-alignments along the line of sight, the
modeling of baryonic clustering, and the presence of diffuse gas, as well as
instrument beam convolution and noise. We demonstrate that two complementary
approaches, aperture photometry, and a matched filter, can be used to recover
an unbiased estimate of the cluster kSZ signal and the associated optical
depth. Aperture photometry requires a correction factor accounting for the
subtraction of signal in the annulus while the matched filter requires a tuning
of the signal template profile. We show that both of these can be calibrated
from simulated survey data. The optical depth estimates are also consistent
with those inferred from stacked thermal SZ measurements. We apply the
approaches to the publicly available Atacama Cosmology Telescope (ACT) data.
The techniques developed here provide a promising method to leverage upcoming
kSZ measurements, from ACT, Simons Observatory, CCAT, and CMB-S4 with
spectroscopic galaxy surveys from DESI, Euclid, and Roman, to constrain
cosmological properties of the dark energy, gravity, and neutrino masses.
