Your argument with the dollars fails on two accounts. First, the "take a penny/leave a penny" concept has one MAJOR security guard that this experiment doesn't have ... a monitor. That monitor being a sales clerk. The second a MAJOR security breach, the anonymity factor.
All arguments to make this experiment analogous to any "Take/Leave" scheme is flawed on these accounts. (Not that I don't appreciate the analogies, I do.) Would Sam (or anyone) have acted the same had they been in the same position with any of the "Take/Leave" assumptions. My guess, no. Sam like the anonymity of being able to take without consequence. Now that he has revealed his duplicity he's not liking the consequences.
All arguments to make this experiment analogous to any "Take/Leave" scheme is flawed on these accounts. (Not that I don't appreciate the analogies, I do.) Would Sam (or anyone) have acted the same had they been in the same position with any of the "Take/Leave" assumptions. My guess, no. Sam like the anonymity of being able to take without consequence. Now that he has revealed his duplicity he's not liking the consequences.