How do travel agents deal with clients who keep changing their budget?

I run into this more with family trips than solo bookings. The client starts with "we are flexible," but after two days of options the real budget is lower, dates are fixed, and baggage or seat fees were never in their math. I have started asking for a hard ceiling before I price anything, including taxes, bags, resort fees, and travel insurance. If they will not give one, I only send a rough…