If you cannot tell the source then it is sure that you have a service of providing fake likes but don't worry because there are a number of people who need only likes no matter it is from real human or from fake systems because they only want to show their business as a bigger company having bigger social media community.
do you think this 75% come from illegal way? like bots or botnet? in this case is very bad and not safe for our business
Problem is not from where are coming this likes. Problem is with Facebook bots. They recognize fake likes even if they are coming from exchanges. I have tested this methods few months ago, and always after 2-4 days all likes disappear. I talk here about
Fan Page likes, not about post/picture likes.
Let see what OP can do.
Still waiting for response.