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I agree, replying is a show of a good manners and etiquette. I try to reply to all the comments made. But upvoting should be left to get the comments you think are exceptionally good to the top of the list.

I saw his comment on another post and thought that it amounted to begging and was in itself bad etiquette. I think you have summed up the situation well as I see it. I have seen one author that doesn't seem to upvote any comments and I find that odd, but to upvote everything means you are devaluing the really good comments because they get the same reward (an upvote) as the "crappy" comments.

I find non-response from the author more disheartening as commenter than lack of an upvote.

Spot on my man! You managed to express my views in a much more condensed way than I did :)

upvoting should be left to get the comments you think are exceptionally good to the top of the list.

On my post's I would let the readers do that, and also not try to identify any comment as the relevant one over others.