The key here is communication. Send them a report quarterly (or even monthly if high activity) indicating services rendered:
1/6 – Spoke with CPA re taxrn
1/7 – Evaluated market status and rebalance of portfolio
1/9 – Spoke with attorney re funding of trusts
1/10 – Reviewed all positions to verify in market versus ahead of market

You get the idea. Like an attorney or any other consultant you should send a statement of services rendered to clients. Time consuming in only that you have to become more sensitive to tracking how you spend your time. The real plus is they “see” the value added, and you can begin to evaluate whether your fees are correct with the billable hours.