Answer:
your self-interest; their self interest
Explanation:
When you make a decision to buy a good, you make your choice in your self-interest. There could be different reasons to make such choices. This could be because the good could form part of your basic needs or because the prices are quite low.
When people make a decision to produce the good that you are buying, these people are making their decision in their own self-interest. This could also be to make money.
