Claes had an unsuccessful political career. In December 1747 he was appointed in the Växelkontoret (Exchange Office), a financial institution created to stabilize exchange rates of the Swedish currency. In the same month Grill was appointed in the Association of Ironmasters. The same men ruled both institutions and that created opportunities for private initiative and abuse of power. In 1749 he promoted a Swedish merchant fleet. In 1753 he was appointed to the SOIC. During the winter and spring months of 1757–1758, the Stockholm bills of exchange market ran out of control. The Exchange office survived until the beginning of 1761. The associates obtained a compensation over 2 million for their expenses. In March 1765 the Caps launched a legal investigation of Claes and Johan Abraham Grill, etc. In 1766 Claes was fined, together with his half-brother. They were accused of conscious mismanagement of the office for their own profit. The Grills sentenced to pay back half a million to the Riksen Ständers Bank. Claes Grill lost his civil and burgher rights. His widow continued to run the Trading House; her son Adolf Ulrich took over the business in 1778.
