It's painful to see those negs and neutrals but if it helps any, they have no effect on eBay's opinion of your selling account.
They do have some effect on the few buyers who actually look at feedback. Not too many since we see a lot of complaints from innocents who think 95% is an "A".
And that particular neg is pretty obviously from a .... (trying to be polite here)... technodolt?
I doubt it will do you much harm.
Now.
In future.
If this happens again, first you contact the unhappy buyer and tell him to open a Dispute .
DON'T PANIC!
You will be required to send him Return Postage. (Unless you can persuade him to send it back on his own postage. But with that guy that might include teaching him how to address an envelope and lick a stamp, so... )
When you get the item back (even damaged) you refund him.
And THEN you ask eBay Customer Service to remove the neg, since by refunding you won the Dispute and the buyer cannot leave feedback.
Except-- you were selling digital products. There is effectively no protection on those since neither buyer nor seller can prove delivery.
Poot.
