Does a coast to coast letter travel by ground/truck or air these days?
Yes, it can be slow, HOWEVER, I mailed a small first class package (get free tracking number) Friday morning from rural San Francisco Bay Area and it was picked up at the POB this morning in New Jersey.
That said, still contact the seller and directly ask when it was sent, confirm the address to which sent and advise it has not arrived. That will alert the seller to a pending claim likely. If the sellers response is reasonable, great; if not, file the eBay
Mail can be delayed, misdirected, misdelivered or unknowingly destroyed.
It happens and eBay
hates paying out for that and is why eBay
wants sellers to ship via a tracking method at an extra cost to the buyer.
Me, just last week I received a priority envelope from New Jersey which contained my eBay
order from Japan which was accidentally addressed not to me but to another client in New Jersey. The seller had alerted me to the issue previously. In this case I received my several hundreds of dollars of goodies as the client is New Jersey was the seller's largest client. There the client's fear of being cut off from the seller was the likely biggest motivator to send me the material if just common honesty was lacking. Of course the seller refunded the $8.95 US Priority cost and then some to that client.
Also last week I received a remailed item which had been returned as unable to forward from an old POB address (I held it for 45+ years and closed it only 3-31-2022) which has a current forwarding order with other first class item being forwarded to me. This time the sender used the correct address, the address I emailed to him five times previously. The original item was sent certified. So sender error and postal error (not forwarding) combined. It happens.