ISFJs do things for other people. It's how they show they care. I think they are sensitive but they don't display those emotions much to others. They hold things in. ISFJ is the stereotypical mother whose life revolves around and does everything for her kids. INFPs are far more independent of others. They aren't as much doers. The INFP will spend a lot of time and thought with a gift for someone - it will be something special even if it is small. Maybe it will have some kind of meaning. The ISFJ will quickly make those buying decisions with the idea that "it's the thought that counts" and not think a great deal about what it is they are getting and how much the other person will like it.
So, the ISFJ is do, do, do. Do your best to make others happy. You should do things a certain way because that is how you do things or how people wish to be treated. They are wonderful to be around. They pay attention to you and are nice. They are judgmental about others relating towards a person's behavior and what aligns with the expected norms.
The INFP is much more of an individual. They are more moody and more likely to be loners than the ISFJ. They are much more abstract and complex thinkers and more of an idealistic and ivory tower type. They are quite judgmental about others but it relates towards imposing their personal values on what is right or wrong - it's less about specific behaviors and more holistic in the judgments that are applied (e.g., how a person lives their life, what their values are, views on problem in society).