eBay will remove the feedback BUT it will still count against you
buuuut don't worry too much because 1) feedback doesn't matter as much as people think it is (Although, when sales slow down, you are gonna SWEAR your recent bad feedback is causing it)
And 2) Feedback is easy to get revised to neutral or positive.
If you want to get the feedback revised, you need to "correct" the situation with the buyer.
Since they weren't happy you sent the item from walmart, I'd say something like
"Hey there. I saw your recent feedback about the item coming from walmart. Many of my items are purchased online. I was not trying to fool anybody. Please start a return case on your item and I will provide you a prepaid return label AND a full refund"
Most buyers are angry because they THINK that you are actively trying to scam them. Show the dude you are willing to work with him and you'll get better responses from him. Unless hes one of the few genuine pricks out there.
Then, once the return is done (or once you've at least had a conversation where the guy is a little less angry)
Go to the feedback forum on eBay and submit a request for the guy to revise his feedback. Ask him something like this:
"Hey. I have provided you with a return label to resolve the situation. I want my buyers to be happy. I had no intention of fooling you. If you could revise the feedback to neutral, I would really appreciate it"
You'll find that if you time your feedback revisions correctly by 1) providing a resolution and 2) waiting a few days after the resolution, you'll be able to convert 50% - 75% of the negative feedback you receive to neutral or positive