How does the Follower selling work?

Hey guys,
I'm not interested in doing this because I like outsourcing, so you dont have to fear a new competitor .
It's just one thing: Im owner of a webshop where I resell this follower services, and there are often people who ask me "how do you win/produce the instagram followers you send me?"
And then I dont have an adequate answer because I dont know also.
So could somebody tell me how this process works?

Thanks in advance

I have a similar question towards a service I provide that is not very common. I simply answer "I apologize, but this is knowledge I acquired through years of study, and is the knowledge that puts food on my table, so I'm not going to disclose my tecniques, you must understand that."
But maybe that is not the best way to do it, maybe someone else has some interesting differing ideas.