28. Specific performance of a contract cannot be enforced against a party thereto in any of the following cases:-(a) if the consideration to be received by him is so grossly inadequate, with reference to the state of things existing at the date of the contract, as to be either by itself or coupled with other circumstances evidence of fraud or of undue advantage taken by the plaintiff;(b) if his assent was obtained by the misrepresentation (whether wilful or innocent), concealment, circumvention or unfair practices, of any party to whom performance would become due under the contract, or by a promise of such party which has not been substantially fulfilled;(c) if his assent was given under the influence of mistake of fact, misapprehension or surprise: Provided that, when the contract provides for compensation in case of mistake, compensation may be made for a mistake within the scope of such provision, and the contract may be specifically enforced in other respects if proper to be so enforced.Illustrationsto clause (c)- A, one of two executors, in the erroneous belief that he had the authority of his co-executor, enters into an agreement for the sale to B of his testator's property. B cannot insist on the sale being completed. A directs an auctioneer to sell certain land. A afterwards revokes the auctioneer's authority as to 20 bighas of this land, but the auctioneer inadvertently sells the whole to B, who has not notice of the revocation. B cannot enforce specific performance of the agreement.