The claim that the cis isomer dipole moment is always greater than the trans isomer is refuted by chemical data showing that trans isomers frequently possess larger dipole moments than their corresponding cis counterparts.
The claim states an absolute rule ("is always greater") regarding the relative dipole moments of cis and trans isomers. Multiple retrieved experimental chemistry papers (e.g., [0] and [3]) provide clear counterexamples where the trans isomer has a larger dipole moment than the cis isomer (e.g., cyclopropanecarboxaldehyde and 1,3-pentadiene). Therefore, the claim is definitively refuted by the provided evidence.