SoggyShorts
Mathematician par Excellence
I'm not a caterer but of the few times I've done it I've had some 50/50 chances where a single spectral stone would have saved me 25 diamonds.So [spectral stone's] usefulness will be very limited unless you have quite a lot of them
There are also some alternative strategies possible where you purposely leave yourself with several possibilities on one Spirit by focussing on satisfying the other 4 since you know you can clear that last one regardless of information.
Edit: oooh and running out of something (like coins) when you KNOW the answer to solve the negotiation on round 3 can be fixed too. Maybe a waste but still....