Wholesalers work with agents question (off market) in California

[Poppy Z.]

Hello, BP family. I am trying to be a wholesaler in the Bay Area California. I sent out 300+ handwriting yellow letters last week and received several calls. And I will send another 200+ next week. 

One of them was from a listing agent. He left a message and wanted to talk to me. I believe that the property does not list on the MLS. I do not know how to work with him. What I should ask and how I deal with this situation? I should stand as a wholesaler or a cash buyer? Is it legal?

Thanks！