Where a broker was employed to secure a loan to enable the principal to prevent a mortgage foreclosure sale, but failed to procure the loan, the relation did not prevent a purchase by him, in good faith, at the mortgage sale, nor raise a constructive trust for the principal on such a purchase. Clark v. Delano, 91 N. E. 299, 205 Mass. 224, 29 L. R. A. (N. S.) 595.