consumerist Christian

A person who tries to uphold modern Christianity principals; eg. don't steal, lie,rest on the Sabbath etc. but who can be overtaken by the what's-in-it-for-me mentality.

David: Here you go, you can have this old guitar if you want...there's no strings either.
Terry: What are you doing that for? I can tell...you'll want something in return one day.
David: You're just being a consumerist Christian again my friend. We can fix it up together if you like.