Market validation means replacing a guess with a written record. Begin with a list: the mandi commission agent, vegetable retailers, a hotel or caterer, a canteen, a processor, direct household sale.
For each one write the name, the phone number, the quantity per week they can absorb, and the pack they want. Then collect one piece of paper from each: a rate slip, a purchase order, or your own dated note with the buyer's name on it.