Gary is the owner of a scallop boat. In 2017, Gary leased the vessel to his cousin, Sam, for 10 years at an annual rental of $10,000. In 2019, it became apparent that scallop numbers were declining, and Sam soon realised that he would be unable to meet the annual rental charge unless the catch improved. He approached Gary and advised him of his fishing and financial difficulties. He also complained that the engine in the scallop boat was not as powerful as he had been led to believe. Gary denied that he had ever made any promises or statements about the engine power. However, he said that he was prepared to halve the annual rental until the scallop catch improved and, accordingly, the rental charge was reduced to $5,000 with effect from January 2020. No document was signed to this effect.

Towards the end of 2022, the catch improved significantly to such an extent that Sam was able to resume paying $10,000 a year. Gary was delighted to hear that, and it was agreed that the annual rental of $10,000 would resume again in January 2023. Gary further advised Sam in January 2023 that not only did he have to pay the annual rental of $10,000 until the end of the lease in 2027, but also the $15,000 forgone by Gary in the previous three years immediately.

Advise Sam whether he must pay the $15,000 claimed by Gary (Do not discuss misrepresentation).