How do you buy power likes? What do you check before buying?

I read in a thread that power likes will only work when if they come from accounts that have in total several million followers.
– So do you try and make a weekly deal with several 1M accounts in your niche?
– What must you check before buying? Any common pitfalls to avoid?
– And once you buy, what is the deal? The big account will like all your posts withing an hour of posting?