This study is flawed. The issue hay it doesn't take into consideration is the timing of WHEN each offering was made that each customer was not in a hurry to not choose more, take the time to order more choices and thus a larger amount and finally no presentation of choice for another set of at least two other donut stores: one very close by say less than 3mins walk vs 5+ blocks away (10-20min walk).
Such a suggestion of yours of a study is not double or more blind nor is using any scientific method at all. This limiting the choice of a user in a study without granting them choice for an alternative makes the study non qualifiable.
