You best bet would have been to look over the tank, say I would remove all these small pumps and skimmers. Add a few waveboxes or streams, get a large return pump, big skimmer and whatever else you felt needed changed. If he said no I would have told him you can not help and to call someone else. Trust me if no equipment is changed then the tank will never look good. There is just not enough flow in that tank.
What I would do from here is make a price list for him with:
1. Equipment and price
2. labor to change equipment
3. weekly water change price for at least 2 months
4. Discount for selling off used equipment
5. Huge bold note saying something about what you are going to do may not 100% fix the tank and more equipment/maintenance could me needed.(cover your butt for all the money he is spending)
I sure there are more but I am just getting moving this morning. I will post more if I think about something else.
Lastly if he aggress to your list/invoice then have him sign it and get to work changing out things.
If he says no then say bye and never look back.
If he wants you to spend hours explaining way all this is needed DON'T just spend 5-10 minutes saying you hired me to fix your tank and to make it look good and have healthy animals you need the right equipment. Do not spend to much of your time on it if he is not going to work with you to fix the problem, you just need to move on, this will save you time now and in the future.