Black-Hole Spin Measurements from X-ray Reflection Spectroscopy: Quality Criteria and Community Recommendations

X-ray reflection spectroscopy provides one of the most powerful electromagnetic methods for measuring the dimensionless spin of accreting black holes. It has yielded spin constraints for stellar-mass black holes in X-ray binaries and supermassive black holes in active galactic nuclei, and is central to the science goals of current and future X-ray observatories. However, the technique is subject to observational and modeling systematics, including continuum-reflection degeneracy, limited spectral coverage, unresolved distant reflection or absorption, detector effects, source variability, accretion-state dependence, and assumptions inherent to reflection models. Motivated by discussions at the 2025 Wake Forest workshop *Recent Progress on Black Hole Spin Measurements Across the Electromagnetic and Gravitational Spectra*, we propose a practical framework for evaluating whether published reflection-based spin measurements should be considered robust, provisional, or not assessable from the available information. The framework is built on three principles: **detectability**, requiring an unambiguous relativistic reflection signal; **uniqueness**, requiring that the relativistic component be distinguishable from the continuum, distant reflection, absorption, and instrumental effects; and **robustness**, requiring that the inferred spin remain stable against reasonable changes in model assumptions, data selection, and accretion-state treatment. We translate these principles into assessment criteria, a quality-classification scheme, and a reporting checklist for future studies. Calibration of these criteria through dedicated simulations is outlined here and deferred to a companion paper. Our goal is to establish a reproducible path toward a community-maintained compilation of reliable black hole spin measurements for the high-throughput, high-resolution era of X-ray astronomy.