Not sure I get your point. Imagine store A is a platform like Booking.com, and store B is seller’s site. There is a complaint every day to store A that store B

Not sure I get your point. Imagine store A is a platform like Booking.com, and store B is seller’s site. There is a complaint every day to store A that store B sells cheaper. Store A charges the customer less but pays the seller the same, taking a loss. Meanwhile, it turns out that those customers are friends of the seller, to whom the seller compensates the transaction plus some extra on top.