As far as the setting on your brake controller goes, there should be a calibration procedure in the owner's manual to get you in the ballpark, then you can fine tune the settings to fit your own personal tastes and expectations.
There is no one right number setting on the brake controller.
If the brake controller is maxxed out, though, and you still don't feel you have enough braking action from the trailer, you have a problem that needs to be addressed.
NEVER trust that someone has "checked" your brakes, because 99 times out of 100 that means a visual inspection. They looked at your tires, and maybe glanced underneath the trailer to see if anything was falling off.