Just because someone has a lot of followers on Instagram doesn’t automatically mean they have any influence over their audience. It’s possible to be a fun person to follow, without having any authority whatsoever. In fact, this is the rule, not the exception.
I’ve consulted businesses who have worked with so called influencers, been kind one myself, and helped people with large audiences get deals with brands, so I’ve seen this from every side. It’s clear to me that most people, including myself, don’t have significant influence over masses of people.
People with a big following simply have the ability to broadcast a message to a large audience. That’s not nothing, but don’t mistake it for influence.
Stay away from paying big money to an influencer based on anything else than sales records of previous similar campaigns. Even then I'd rather just offer a generous commission.