First of all, thanks for all the advise.
Here is my story.
I ordered some samples (40 units) from the plant. Then post my ads. A local business man called and said he wants about 5000 units and asks me if I have them. Abviously he wanted to pick up goods from me directly. But I don't have them and I want this business. He will come to my office tomorrow. I am trying to figure out a way to handle this situation. For sure I will be honest. But what is the best way to deal with this kind of problem? Many many thanks.