I've interacted with people that sell that service for a while and I can say with utmost certainty (or at least beyond a reasonable doubt), that only 1% of people selling that service are legitimate. Anyone selling Verification services for less than ~$1,000, is a scammer. And on top of that, you must do you due diligence on checking their background.
These are people with an inside man/woman, who have agreed to this deal on the basis of a business relationship.
But, Instagram started taking verification badge requests for a little while now.
There are no guarantees, but the main thing is having a presence on the internet in general. The bigger your presence can be noted (outside of the platform), the more likely you are to get approved. This means maybe having a blog, or guest posts on other blogs. Possessing other platforms with a decent sized audience, a website, etc.
One of their criteria even states;
"Notable: Your account must represent a well-known, highly searched for person, brand or entity. We review accounts that are featured in multiple news sources, and we don't consider paid or promotional content as sources for review"
The blue badge is supposed to be a signification of social proof. So you need to have evidences proving that you are to an extent a public persona.
