Just leave the buyer negative feedback and state why.
If it's such a big deal for you to not hear 'Ah gawtcher naf inna mayul!' that you're willing to put someone (who didnt cause you problems or tie up your money or goods with drama otherwise) on the blocklist, use the feedback mechanism given to you to warn others their transaction with the person may be as bad for them as it was for you. Clearly, you dont come across as though you're 'satisfied with the deal' without that final email.
Maybe?
Or if its a huge deal to you, ride that tracking info for yourself. Nobody is stopping you from putting that number in your own browser to see what's up. Before you say "it's not my responsiblablabla", stop and think about who's whining about what and why. If you want the info, you can retrieve it yourself. Remember, you troubled yourself to: post item for sale (likely in a few forums, cross posting is popular here), execute a deal with more than a few communications between yourself and the buyer, arrange payment thru third party services, pack the item, and ship the item. Why not just make sure it got there after a week, too? Hell, have usps send you delivery confirmation. They do that these days, I dun bin told.
Otherwise, hike your own hike - always send YOUR thank you note and feel all warm and squishy inside because you're 'better' than those rubes who didnt acknowledge you in the past. Or whatever your deal is.
It's unlikely that you have anything the knife world can't live without or doesn't have an extra few of, so ignore away if that works better for you.