I have been offered a verification that costs less than a Cofrac calibration. What should I do?

By referring to the definitions of calibration and verification, you will notice that it is usually preferable to proceed with a calibration before being in a position to perform any verifications, according to the terms in example2. Inthis case, it is difficult to claim that a verification costs less than a calibration. The second part of the question is about calibrations performed by accredited laboratories. It is quite possible that non-accredited laboratories propose verifications that cost less than the calibrations proposed by accredited laboratories. If you use a non-accredited laboratory, then the normative requirements impose a number of actions in order to evaluate your subcontractor (see "La métrologie un outil pour la qualité" (Metrology: a tool for quality), available in French and English, on the publications page of this site for more information on the assessment of calibration or verification service providers).