Exclude members of a group from User Criteria

Hi all,

We have a category on our Service Portal which uses a User Criteria to ensure it is not available to users of a certain Company. However we have a need to update this criteria to exclude users that are in this Company but are also members of a certain user group.

I have tried to add a script to the User Criteria to check the current users group and return as false if they're a member of the group but as you can guess this doesn't seem to be working. Is my script sound or is it a limitation that I wont be able to work around?

function checkGroup() {
    var retVal;
	var currentUser = gs.getUser();
	
	if (currentUser.isMemberOf("Tech IAM team")) {
			retVal == false;
			
		}else{
			retVal == true;
		}
	
	return retVal;
	
}
checkGroup();