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I dare to say 100% of the bidbots are not profitable. In order to be you need a vote 225% larger than your bid. Take a look at this tool. Go to details for the last rounds and see for yourself.

For more information I dedicated some articles, going from Hype to disbelief, now I know how they work and I do not use them at all.

Check; https://steemit.com/steemit/@santana33/steem-robots-stop-losing-money-and-how-to-be-a-pro

I will write another post on this matter, besides if you want support SmartSteem.

Most of the bots are actually bid on for too much by everyone so they usually result in negative immediate ROI, you can check on steembottracker.com and see their last bid window to verify. Only a few bots have guaranteed positive ROI, but they often have stricter rules for posting.

The main purpose of bots from the consumer standpoint should be to get visibility and hope for others to vote on your post through the quality of the content, so it's kind of a gamble no matter which way you look at it, considering the price of steem or sbd is always fluctuating and could be higher or lower by the time your post pays out.

It is about Math, they have open source code and you can check how many bids there are.
It depends on the ability of the end-user whether or not they are profitable. Of course, there are a few issues, like last minute bids that can throw even smart bidders off.