Ask how long they have worked with the same community, who leads the projects locally, exactly what your fee covers, how big the groups are, what happens to the work after you fly home, and whether the projects were requested by the community. Honest organizations answer all of that without hesitating.
How long in this community? Who runs the work locally? What does my money cover? Who else is in my group? What happens between trips? Is the work community-requested? How are children protected? What do past travelers say?