Conscious inaction; an action in itself?

[Kilroy_x]

Yeah, I guess I needed to make a topic like this... so, here it is.

Warning: Needless hypothetical situation as vehicle for concept follows.

A person walks into a store and browses around, as people frequently do. He sees a product for sale and contemplates buying it, but ultimately decides not to do so, leaving the store. The store owner retains the product and the person retains his money. Now, it is surely true that the decision to refrain from the purchase constitutes an action, but an action in what sense? Can we claim it is an action which is causal in nature? There seem to be two states of affairs which correspond to the decision, namely the retainment of money on the part of the would-be shopper and the retainment of the product on the part of the would-be seller. However, the money was in the hands of the shopper to begin with, and the product the hands of the merchant. Nothing has changed as a result of this action.

Now, let's look at another situation. In addition to the first person walking into the store, another person does so as well. They have the observable intent of buying the product. However, if this person buys the product they will use to to, I don't know, let's say to make all mashed potatoes slightly less delicious tasting. In this instance, our not quite propagandistic nameless scenario person has to decide whether to buy the product before the other person, or to let events take their course. He chooses the second option. Is he responsible for the actions taken by our mild annoyance causing nameless scenario villain? He didn't fulfill any active role in establishing conditions which would lead to the actions of the second person. All he did was refrain from rearranging conditions to prevent a course of action.

So, the question which in this scenario is grave as gravy is, did our random person violate a duty or the rights of others by conscious inaction, and if so how is this derived?