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One thing that is important to note: the bot tracker uses live prices of STEEM and SBD, but upvotes use the official STEEM price as published on sites such as steemd.com. It is that difference that can have either a positive or negative effect on the calculations as seen on the tracker.

One other thought: you need to make it crystal clear which ROI you are guaranteeing, before or after curation rewards have been deducted. A small positive ROI before curation rewards are deducted will still result in a negative ROI after deduction. that all sounds very fair to me, but I suspect not everyone understands all the numbers on the tracker! :-)