I have a customer facing role, then it's easy to get questions about details that I don't know from the customers. My approach is easy: always being very transparent. I can say "I am not 100% sure, then I will verify with my colleagues and with R&D and let you know" or just "I don't know right now, but I am taking notes and let you know ASAP". This approach also helps me to ask the right questions to the customer, just to understand what the customer wants.

I was on the other side for years and I hate when consultants try to avoid the questions or give me foggy replies.