Came here from the comment that ScribScribScrib made.
There is a massive amount of spam on Reddit that most people would very quickly recognize as spam. For those who do it, good luck because you're going to churn and burn through accounts and domains like crazy. Moderators deal primarily with this type of spam, sending the reports to admins who blanket ban accounts and domains. This is probably unprofitable and if there is a profit, it probably isn't much, plus all it takes is a change to Reddit's algorithm and it would dry up in a second.
There are far less obvious posts that do make it through the initial filters but are taken down as spam pretty quickly. The moderators on Reddit are smart people, they know what to look for when determining if something is there naturally or artificially. It's pretty obvious to me when I see something that is there artificially. Sometimes it stays up, sometimes it ends up being removed.
What I do is take what I've learned and make it appear as though the content is there naturally. I do this for my own sites, I do it for client sites. Way WAY more goes into a Reddit post behind the scenes other than a link and upvotes. I've had people balk at my price (it's one of the more expensive services here) because " I can just post it myself and upvote it myself". You sure can, and it doesn't matter if you upvote it twice yourself or send a couple thousand at it, the vast majority of the time, the second a moderator sees it, it gets removed. Then they come back "Well I can give you $50 for the service, not bad for 10 minutes of work", and I laugh to myself and politely tell them the price is firm and it takes far longer than 10 minutes. Most of the time, that's the end of their Reddit marketing.