There are certain tools you can use to see if the app/platform takes benefactor rewards: https://steemworld.org/@youraverageguy
dmania - they take a cut
zappl - I am not familiar, I'm not using it
busy - if you use them to create posts with busy tag they upvote your post (the strength of upvote is determined by steem power of your followers) do they take a cut, I don't know
I hope this helps a little.
RE: Am I Being Robbed By 3rd Party Steem Apps?