Tim
Well you see the way that I answered the people in my situation, I knew that they got my message as they were almost forced to respond to me or possibly face a law suit so they acknowledged that they made a mistake. I then knew that I didnt have to block them.
In your case, you dont know if the guy believes you or not and whether he now understands how the bidding process works or thinks you cheated him.
On the other hand, if you come across another widget similar to what he was bidding on, and he is now aware of what they are selling for, he may in fact bid high enough to win it, so why block him?
Well I suppose if he is stupid enough to only bid $4 again and looses out to another bidder, he may escalate his accusation and take it to eBay the next time.
I just feel that if I am accused of something, it is important to deny it in a response, so even if you explained the bidding process, I would hope you at least denied his accusation in your email to hi, as well.
OK, here is my feeling on whether you should block him or not:
If he doesnt respond to your reply within another 24 hours, block him! He might repeat what he did and take it up another level which could cause you some problems and certainly waste your time.
If he emails you and thanks you for the time you took to explain how eBay bidding works, then dont block him, he will probably turn out to be a greatful eBay that may tunr into being a good customer, appreciative of the time you took to help him.
Malcolm