It's one thing to upvote you own content manually but to set bots to upvote your own content, that is greedy and taking an unfair share of the total rewards pool.
To buy your upvotes for your own content, I'm not sure about, but it's your money you are risking....some even don't get a good return...but the businesses runnning the buy your upvote services do I'm sure.
It is mostly whales running those services to 'help' the minnows. Remember they are a business, and the aim of businesses is to profit.