This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
If the identity of the adversary party is not material, mistake therein does not affect the validity of the contract.1 Thus where A was ready to contract with anyone having authority to lease a certain canal boat, he could not avoid his contract because he was mistaken as to who the real owner was.2 So if A makes an offer to B, and C delivers his own property in performance of the contract, A can not avoid liability under the contract if he knows that C is delivering his own property.3 A principal can not refuse to pay commissions to his broker because the latter has concealed the identity of the real party from his principal where it does not appear that his identity was material.4 If the offeror knows the offeree, and gains whatever benefit he contemplated from the character and substance of the offeree, he can not avoid liability to the undisclosed principal of the offeree on the ground of mistake, even though the offeree was acting as agent for such undisclosed principal.5 The fact that the offeror's agent does not disclose to the offeror the fact that the offeree is acting as agent of another does not authorize the offeror to avoid such contract.6
1 Shenberger v. Union P. R. Co., 84 Kan. 79, 33 L. R. A. (N.S.) 391, 113 Ac. 433; Chicago, Milwaukee & St. Paul Railway Co. v. Greenberg, 139 Minn. 428, L. R. A. 1918D, 158, 166 N. W. 1073.
2 United States. Texas & Pacific Ry. v. Mugg, 202 U. S. 242, 50 L. ed. 1011; Kansas City Southern Ry. v. C. H. Albers Commission Co., 223 U. S. 573, 56 L. ed. 556; Adams Express Co. v. Croninger, 226 U. S. 491, 57 L. ed. 314, 44 L. R. A. (N.S.) 257.
Alabama. Emerson v. Central, of Georgia, Ry., 196 Ala. 280, L. R. A. 1916F, 120, 72 So. 120.
Kansas. Schenberger v. Union Pacific R. Co., 84 Kan. 79, 33 L. R. A. (N.S.) 391, 113 Ac. 433.
Minnesota. Chicago, Milwaukee & St. Paul Railway Co. v. Greenberg, 139
Minn. 428, L. R. A. 1918D, 158, 166 N. W. 1073.
New York. Pennsylvania R. R. v. Titus, 216 N. Y. 17, L. R. A. 1916E, 1127, 109 N. E. 857.
Pennsylvania. Central Railroad Co. v. Mauser, 241 Pa. St. 603, 49 L. R. A. (N.S.) 92, 88 Atl. 791.
1 England. Smith v. Wheatcroft, 9 Ch. Div. 223.
United States. Dunbar v. Weston, 93 Fed. 472.
Massachusetts. Veasey v. Carson, 177 Mass. 117, 53 L. R. A. 241, 58 N. E. 177.
Minnesota. Haines v. Starkey, 82 Minn. 230, '84 N. W. 910.
New York Hand v. Power Co., 167 N. Y. 142, 60 N. E. 425.
2 Dunbar v. Weston, 93 Fed. 472.
3 Randolph Iron Co. v. Elliott, 34 N. J. L. 184.