(this post is a feed post from my comments on reddit)
r/business
1. find out where they are getting these things now, for how much and how often
2. find out why they chose this option and what other options they have considered
3. find out if there are particular things they inspect for from suppliers, permits etc.
4. find out what the current suppliers are neglecting or frustrating the customer about
if you can answer these in detail from 10+ potential clients, you can consolidate the answers and see if theres any opportunities.
your customer have all the answers, but you have to be masterful in getting the answers from them, and creative in providing the solution.