If you do a favor/gift for a stranger, do it because that's who you are. You are a lovable and kind-hearted person and this is an opportunity for you to share this love and kindness with the people around you. Your actions should be a reflection of who you are, not a reflection of how the people in your life do or do not treat you.

Do not perform acts of kindness, with the expectation of them being returned. It's really silly to do a favor for somebody just because you need to get something from him/her in return. Other people can notice it, and they can feel that you are not doing the favor because you care about them. Therefore, you won't feel the inner hapiness of giving to other people. Because giving to other people makes you feel an inner happiness... I personally wish that we all feel this inner hapiness, because this is what will keep us going when we are facing difficulties in our life...