How can you differentiate between a person who's doing something for Hashem and between someone who's doing something for himself?
It's pretty easy. Here's an example:
A yeshiva boy, a soldier or another guest walks into shul on Friday night. They're obviously visitors and they don't yet have an arrangement for the Friday night meal. "Reuven" greets the guest and invites him for dinner. The guests politely declines, saying that "Shimon" already invited him.
If Reuven is a real giver who's doing something for Hashem's sake, he'll be happy that the guest has a place to eat. If Reuven is doing for his own ego or prestige, he'll be disappointed that the guest will not be eating at his house.
The same goes for Outreach. A true Outreach organization doesn't care how people get close to Hashem, as long as they get close to Hashem! A self-interested organization only wants people to go through them - everyone else is no good. That can't possibly be true Outreach.
The "real giver" law applies to all aspects of life and interpersonal relations. Keep it in mind, for it wll give you a much clearer insight into people's motivation for doing things.