New here, but it doesn't seem right to have any selling or buying votes. I am also, thus far apprehensive to down vote anything (not that it would matter) because I dont understand what it would do. Why can rewards be based on creating something good and useful (for example small advertising that cuts out the middle men such as google or facebook, based on views and likes by steemit users and the casual people who happen to find the content on a search engine). The steampower holder would still get interest or a proportional share or created blocks, but not have total control over what qualifies as good material. Not even sure if changes are possible, or if details like this are locked in forever. Just random thoughts from a new user, take them or leave them. Also, If your content gets massively and unfairly downvoted, cant you just post it again and hope for the best?
There are a lot of issues on Steemit. Some of the problems are not so easy to fix. If the bots didn't practice selling votes openly as they do, then it would be done in secret, hush hush like, and then it would be even more difficult to identify abuse.
As far as you giving downvotes, on Steemit, I go with "when in doubt, don't". Do some research on what the downvotes are for, and what they do. It should be covered in the FAQ.
Advertisement on Steemit will never happen. That is one of the points of this platform in the first place.
Self voting is an issue, but if it wasn't allowed, then people would just make multiple accounts, post with one account, then upvote it with a different account (people are doing this anyway). There are a lot of loopholes. There are people working on these issues, though I don't know the extent. But these problems are why the platform is in "Beta". It isn't perfect, but it is a Beautiful place. Behavior like that of grumpycat and his alternate accounts greed diminishes that beauty in ways that I just can't put into words..