Testing a paid diagnostic call before I build the full offer

I have spent six weeks building what I think agencies need and have nothing to put in front of a buyer except a deck. So this month I am selling a 90-minute paid working session instead — they bring a real summit brief, I map the programme architecture live, and they leave with the plan. S$400, five slots, capped so I can actually watch what happens in the room. Curious whether the payment is what makes them take it seriously, or what makes them not book at all.