The package shows delivered to "MEDFORD, MA 02155 ". That, to me, looks like a post office box number, not a street address. Are you sure that you gave your correct mailing address? Double check your mailing address in Ebay. That might be something that will shed light on the subject. Also, contact the seller and ask him to tell you what address he shipped to.
If the shipping information is correct, and you have checked at the post office to no avail, let the seller know of the not delivered status. If it were me, I would also let him know that I would be filing a complaint with Ebay. Also, what feedback report does the seller have? If 100% good, he is probably telling the truth. If he has had issues before, then the question of honesty can be considered and challenge, if you wish.
Other than that, I have no further advice to offer. Sometimes the mail fails but in over 500 transactions, through Ebay, not one time has an item failed to reach me or a target destination. Let us know how this turns out.
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"98% of the bikes I buy are projects".