I'm guessing his comment is a bit more like "THESE GUYS SUCK!!!!1111111" than "I had to pay $1.44 more for postage". IMO that is fair enough, he is in the wrong. OTOH I'm sure eBay have a process in place for this - I think suing him is a bit much.
They could also just leave him negative feedback...
Buyers and Sellers leaving feedback for each other doesn't necessarily carry the symmetric property of equality. A Seller has more to lose or gain from feedback than a Buyer does.
They could also just leave him negative feedback...