According to Gneezy and Rustichini the presence of an extrinsic reward in activities with a level of intrinsic motivation (e.g. volunteering) reduces intrinsic motivation, thus it may determine opposite results from the expected.
I wonder whether there is any research about the effect a price may have in crowding out intrinsic motivation compared to a fine. Michael Sandel faces this topic in "the moral limits of market", however he does not provide any empirical evidence. Do you know any research that can be used to support this thesis?