I would be asking a few questions. 

1,  Did the seller ask if you were okay with them hand delivering?

2.  What sort of distance are we talking about?

3.  Were you inconvenienced in any way by the delivery?

I would always ask the buyer first before hand delivering, I don't allow buyers to pick up because I value my privacy, I would expect my customers might feel the same.    If the seller had to travel any sort of distance, more than a few kms perhaps, then I would not think it inappropriate that they keep the delivery fee I would have paid willingly when the item was to be posted, especially with a fragile or awkward item that might be inclined to suffer damage in the post.  However, if hand delivery meant I had to wait around for the seller when I may have had other places to be, then I would not have agreed to hand delivery in the first place.

Bottom line, I don't think a buyer can complain about the postage charge they paid being retained by a seller who delivers in person (provided it isn't someone who lives in the same suburb).  Clearly the buyer was happy to pay X amount for delivery, and regardless of the method of delivery, that is what they got, so there is nothing to complain about, unless, as I said, they seller didn't first seek permission, or failed to show up when arranged and kept the buyer from other business.