Thanks to all - its now clear that it is the operators terms being passed on by the broker (who we use a lot), not the broker setting them. We all know canx terms are 'flexible' but it just raised questions when we had never seen anything more than 10% on any charter we had done before - but its now clear.
On the topic of tagging on other flights and not wanting to be exposed - having searched through old posts on here, there’s some interesting thoughts by operators who price the 'empty' leg at mid way between the cost of performing that leg in isolation and the true sale of the leg in isolation. Therefore meaning that should the first trip cancel, the operator still covers their costs and the customer still sees a discount from the 'normal' sale price of the second trip.