Any person who willfully participates in any act or transaction in violation of Section 25400 shall be liable to any other person who purchases or sells any security at a price which was affected by such act or transaction for the damages sustained by the latter as a result of such act or transaction. Such damages shall be the difference between the price at which such other person purchased or sold securities and the market value which such securities would have had at the time of his purchase or sale in the absence of such act or transaction, plus interest at the legal rate.