Client wants to offer $400k over asking

Hi everyone!

Newly licensed agent here!

I got an Op City referral the buyer says he is a cash buyer who likes the furniture so much that he suggested that he offer $400k over asking.

I want to show him the house, but want to ensure that he’s not lying and wasting my time for a free house tour. Can I ask for proof of funds before showing it? I’m in Pennsylvania. Thanks in advance!