Some agents do charge an administration fee if you cancel. This is because they have time and cost involved and will get paid nothing when you cancel. However; there still are a lot of travel agents that charge no fees at all.
This is something we have argued with our TA over. We have changed cruises twice. We know she has a small fee for those that cancel. We agree with that. The two cruises we changed took extra work on her part, we expected the fee, it was not charged.
She would not take the money saying we did not really cancel, we were stilled booked... both times we dropped of a gift card for dinner.
A good TA earns every penny they get.