It sometimes happens that a seller, acting with the utmost good faith, is unable to comply with his contract, and under such circumstances, he becomes liable to the purchaser for the return of the deposit, and for the reasonable expenses of the examination of the title. The amount of these reasonable expenses is an uncertain quantity, and it is prudent for the seller to specify, in the contract, the amount he should be called upon to pay, in addition to the return of the deposit money, in case the title be rejected for a valid reason.