The saying “the customer is always right” is simply not always the case.
Sometimes it doesn’t make sense from a financial perspective to do what the client wants. If it’s not economically feasible the best solution is simply say “no” and agree to go in different directions.
Other times it’s best to say no when you know what they are asking for is wrong or wont work. While doing the wrong thing might benefit you short term, when things fall apart (and they will) it becomes very easy for them to place the blame on you.
If you know you are being asked to do something that is wrong, be wiling to stand up for your beliefs. You might be able to change their mind but even if you can’t, you then know you can walk away having made the effort to do the right thing.
Have a great day!