in some transaction for
in (something) for (someone)
Involved with or a part of something in order to benefit from it. Why should we help you? What's in it for us? A boost to your resume is in it for you if you take this job.
See also: for
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
in some transaction for someone
having value for someone; having a benefit for someone. (Usually a question: What's in it for me?) What is in this deal for me? There is a lot of money in it for you.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.