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How do you check it out? The curation rewards (the 30-minute rule, f example) and the different rewards (SBD; STEEM and VESTS [SP]) always confuse me when I'm calculating the ROI.

Via steem world.org you can check what amounts someone transferred to paid upvote bots. Or you can check his wallet, that provides of course the same info. And then you check his pending pay out.

Of you use steem world.org you can check power upvote the pending pay out value. That makes it a bit more easy to see if buying an upvote was profitable or not.