Did you go to the post office with a copy of your eBay order to show the clerk the tracking number and your mailing address - then ask them to check the package on their internal system to see if 1) the tracking number was addressed to you and 2) if it was addressed to you, what the GPS coordinates are on the delivery scan?
If it was addressed to you and misdelivered then the carrier can attempt retrieval or an insurance claim can be filed assuming the $6 item was shipped with Ground Advantage.
If it was addressed to someone else in your zip code, that's a scam so you'd have to get a signed letter on USPS letterhead that says the package was addressed to someone else (you don't need that person's name address, just a note that says it was not addressed to you) then use that document to file a claim on eBay.
All that advice assumes this is a regular package.
If this was an eBay Standard Envelope (ESE) shipment with an ESUS tracking number then disregard the above advice. If it was an ESE shipment, see below:
eBay Standard Envelope (ESE) is a metered mail shipment so it does not receive traditional tracking scans like a package would, and the clerk at the PO counter cannot scan it or track it. The envelope is scanned by sorting machinery at distribution centers along the way.
With ESE, a 'delivered' scan generally occurs at the last USPS sort facility before it gets to the buyer, so typically the buyer will receive their order a few days after the delivered scan.
If you just saw a delivery scan today then I suggest giving a couple more days for the envelope to turn up.
You can sign up for USPS Informed Delivery. You get an email every morning with images of letter mail you'll be receiving that day (ESE should be pictured with the letter mail), and the email will also show a list of package tracking numbers arriving that day.
https://www.usps.com/manage/informed-delivery.htm
When an item is pictured on your informed delivery email, but that item isn't delivered, you can log in to your account at usps.com and report that you didn't receive it. That alerts the PO and they will alert your carrier that a mail piece was missing from your delivery.
