Gamer psychology, perhaps too optimistic, alternative perspective to enforced rationing.
There is certainly precedent for modern apps using a tips system, not to mention a long standing appreciation for "pay what you want" business models if the customer base has a skew towards overvaluation.
Tip increment or default probably the same as minimum Scales purchase. I think you can "feel" the difference with this way of thinking though, comments welcome and perhaps I am too optimistic about people.
Under consideration feature