You work for a state-chartered bank, and are not subject to federal governmental procurement regulations (e.g., the FAR). You're conducting a pre-response conference with the sellers for an RFP that has just been released.

One seller lingers after the conference and approaches you. It's a seller you've done business with in the past. A further complication: the seller also happens to be a large customer of your bank. None of the other sellers are customers. The seller asks you out to lunch, indicating that the he would like to discuss the RFP.

What do you do?