Carbon monoxide (CO) has gained attention as a potential endogenous signaling molecule, leading to a growing interest in developing fluorescent probes for CO. Many studies use chemically reactive CO-releasing molecules (CORMs), particularly CORM-2 and CORM-3, as CO surrogates, even though these Ru(II) complexes are chemically reactive and release little or no CO without a strong nucleophile and/or reductant. Such reactivity has led to reports of probes that respond to the CORM used rather than to CO. A recently reported RBF-Fe(III) probe was said to detect CO through binding to Fe(III). However, CO is known to only bind to Fe(II), not Fe(III). Further, the study used chemically reactive CORM-3, which is known to cause problems in assessing “CO probes.” Therefore, we conducted a reassessment of this CO probe. RBF-Fe(III) was found to only respond to CORM-3, not CO. Further, RBF-Fe(III) showed time- and agitation-dependent, sodium ascorbate-induced, and cysteine-induced fluorescence changes. These findings indicate that RBF-Fe(III) does not sense CO and highlight the need for caution when using chemically reactive CORMs to assess CO probes.