If you can link a seller to a commander account, let FD know.
That's probably the hard part. Unless someone is being stupid and announcing their commander name, tricky for FD to tell who is doing it. Plenty of people use FCs to help others out.
It was always a concern though and one of the reasons people have been against players being able to transfer credits directly, and was a concern when it turned out FC owners could set their own prices for goods.
You can also report the posts/sites which are doing this just in case FD are not aware. Maybe they could spare some resources to pose as buyers in order to shut these people down.