Depends who chose the carrier/ shipping method and paid for it.
I don't imagine the collector just decided to pay for shipping just out of the goodness of his heart for a transaction he (afaik) was getting nothimg from aside from helping to future proof gaming history.
So, if Byuu didn't want/ couldn't use legit shipping level (most carriers, like DHL here, for cheaper rates, will use local post office delivery when its just a "drop at your doorstep or hold at post office" level.
It's very much likely to be 100% on Byuu, unless for whatever reason the sender -was- paid a good amount by Byuu to cover a good shipping rate w/ insurance, but he cheaped out to make a buck on the transaction.
Now, I imagine the Collector sender ought to be pissed off, and he really should be the one raising a stink with DHL as he is the customer (sender).