Answer:
This is an example of incentive.
Explanation:
An incentive is a motivator to do something, usually by giving a reward or reducing a cost in a transaction. In this instance there is an incentive to buy more goods from the online store in order to avoid shipping charges of $10.
Although nobody in the house needs the $5 doll, it is purchased to avoid the shipping cost. For the buyer it is a good trade-off as he is spending $5 less than he should.
