No offense, but I find that many of you are making assumptions rather than testing it yourself or sharing stories of actually getting banned for buying upvotes. No, you don't get banned on Reddit just for buying upvotes, UNLESS Reddit can prove that you as the poster did indeed buy those upvotes. If Reddit banned all accounts that had botted/purchased upvotes applied, then who is to say that if I want to get somebody banned on Reddit, I'll just buy mass upvotes to them then report them? Not to mention that Reddit has bigger fish to fry so unless you buy 10,000 upvotes at once in a short period of time, there's a solid chance they won't even investigate. But to play it safe, as long as you buy like maybe 100 upvotes, you should be fine. I've seen people get away with buying 500 upvotes in a 5 min span. Most subreddits only need like 50 upvotes to reach the front page of their respective subreddit so you can easily buy upvotes and stay under the radar.
The reason you get shadowbanned is because you were on a bad IP, posted something foolish, or used posting bots. You likely won't be banned JUST for buying upvote services. If Reddit finds you did that, they would let you know via message that you were flagged for vote manipulation.