Hi,
Based on my experience, If the proposal is very good to decline, then better have two chits; wrapped different colour flower inside. Place it in your kula deivam temple in front of the deity and ask a third person to take one, if the colour you wished appears, then better go ahead.
or in villages even today a lime is placed on the goddess head and with the help of udukkai the musician beat the udukkai, if the lime falls in the front of the goddess then it is a green signal for the work to start else it is a red signal.
This one is based on my experience alone.