Buyer says item not received and left me negative review

[fast_c5]

I sold a $3.50 car part that was shipped 1st class USPS purchased in PayPal.  1st class mail does not include a tracking number so I provided the receipt to the buyer.  I place a lost mail claim with the USPS.  After a few days the buyer said they didn’t receive the package yet so I refunded the $3.50.  
After all that the buyer left me a negative review blaming me for the USPS problem.  I requested that the negative review be removed and eBay refused stating the feedback did not violate eBay policy.  I realize eBay is really hands off on most customer service issues including not really looking at the entire situation but after a person requests a review to be removed I would think a better look would take place.  

[wooden_flower]

If the feedback does not violate policy, eBay will not remove it, so what good would additional review do?

You listed the item with free priority mail but sent it as a letter with no tracking.  Since you were never going to be able to show delivery, you should have refunded as soon as the buyer complained.  That is the price of sending without tracking.

A small hard object is not meant to be sent in a letter - the high speed sorting equipment will rip the item out of the envelope, or just chew up the envelope. Sometimes it will get through, but that will usually be the exception.