Because the Democrats wuv you and want you to be happy, the banks are required to make funds available to you within three days of depositing a check.
But if the check doesn't actually clear the other bank, they'll suck that money right back out again.
So that 'certified check' (likely) has something wrong with it. And while you might think it's 'cleared' the bank when the money shows up on your account on-line, the truth is that you don't find out for much longer.
If you really wanted to waste time playing with the guy's head, take the check and when he calls say "oh, the bank has made the funds available to me, but they tell me that it hasn't actually cleared yet -- I'm waiting". But it'll just waste everyone's time, and his time is less valuable than yours.
Or say "Sure. I won't be there, but my neighbor Bob from the Fraud Investigation Unit said that he'd be happy to take the check and take a picture of your shipping agent to boot".