I think “resteem” “share” and exchange upvote are different. We have Resteem and share button. It helps your posts get more visibility. The more people can see your post, the more likely your posts get more upvotes (if people like it). If people dont like it, no matter how many time you share or resteem, there will be no upvote. Right? But “exchange upvote” seems to not be like that. People dont care your posts, no matter what your content is, they just upvote for upvote in return. In short, the difference here is how many people really like your post and vote you because of your content. Resteem and share may get that point, but exchange upvote will never get it. That is why I said exchange upvote is somehow just same with buying vote.