You got one for here. I think it's really case by case. The people who are abusing it are obvious. If it is one comment a day, it's fine. If it is 10 and from a private account that is suspicious.
SBI is a very social example of a comment upvoting and probably the better of the services that do it. It's also not self voting or vote trading. I don't really know other examples because I don't use them and am not 100% sure how they work.
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Thanks for your reply @abitcoinskeptic and perspective. I personally think this ...
... is the key. A "private account" ... Hopefully most Steemians are familiar enough with the SBI accounts to make the clear distinction.
I wouldn't be too worried. Most people avoid downvoting unless they are sure. I just ignore them unless I get a comment or really feel like I'm being targeted. Some people panic at the slightest downvotes that don't even take 1% off their rewards.
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