Ebay sent a revised 1099-K after I filed taxes. The change was the gross amount went DOWN by $12. Do I really have to refile my taxes over this?

It depends.  If it changes your tax due then yes, you need to amend.  You are able to e-file amendments, so you no longer have to print and mail the amendments for the most part. 

Do I need to amend?

So I do not have to refile if it makes my amount owed go down? 

For a change in income of $12 less than originally reported, an amended return should be filed in order to file the most complete and accurate tax return.  But, you are not likely to see any repercussions from the IRS if you do not file the amended return.  

@mueller_jl