I bought accounts here on BHW some time ago and I can assure you that they are all upvoted and at risk of being banned.
My advice is this:
1) Don’t buy accounts that don’t have comment karma.
2) Be very careful: if the account has only one post and one comment, it’s definitely upvoted, so avoid it.
3) Buy accounts where there are more interactions; this suggests the account is more likely to be natural, considering also the cost of proxies.
A 6-month-old account with more than 50 comment karma costs around $10, so it’s affordable. Prices have dropped significantly.
Another thing you need to consider is where the post or comment is placed. If it’s posted in a subreddit with 10,000 members and no moderation and it receives 1,000 upvotes, you should assume that something is not right.
An account that has 4–5 interactions in large subreddits doesn’t need the kind of “insurance” you’re talking about, because it can’t be reported by Reddit; otherwise it would get banned.