I don't think the number of followers is a reliable means of determining if an influencer is reliable or not a scammer.
In this advanced technology, people have taken scam to an advanced level whereby you need not only single fact to take before assuming any influencer to be a genuine one, they can manipulate the review if that's what you're taking into consideration only, they make use of trust pilot as well to influence anything they want.
How long the influencer has been in business can be a good indicator but you should also be careful because his account might be hacked or cloned to carry out a fraudulent act.
Don't always trust anything you're coming in contact with for the first time, the most difficult task to do is to identify an unknown enemy, how do you ensure you make a proper research in knowing those coming for good and those with bad intention, this is where we all fails most time in our assumptions.