Those aren't "extra dollar bills in your wallet" any more than a tax refund is. You still paid, you just paid less. In the case where you didn't go back, you'd have had even more "extra dollar bills in your wallet."

An (absolute, not relative) reward for good behavior — i.e. a positive-ROI outcome for doing the right thing, vs. not doing the right thing — would be, for example, if you came back and told them you didn't pay, and so they gave you the drill bit for free and also gave you a nickel. Any less and it'd just be "no reward, no punishment."

The parent you were responding to stated that people are not really rewarded for good behaviour after childhood. I'm not saying your deed was not a good one. I am saying that you are monetarily worse off for having gone back to pay and that feeling of having done the right thing, or the discount off the original price is hardly an example of good behaviour being rewarded, especially when you compare the reward for not doing the right thing. If there is only right and wrong and the reward for doing the wrong thing is greater than the reward for doing the right thing, then there really is no reward for doing the right thing.

Absolutely agree. I'm not trying to say that everyone should start stealing things because it's _cheaper_, just that the "reward" of doing the right thing is not particularly compelling if someone is already partaking in the bad behaviour.