On Gmail, I'm firstname.lastname@example.org
Some other guy with an account on eBay has a registered email address there of email@example.com (note the full stop).
Gmail is sending his email to me. So maybe nobody is answering the stream of questions about what I am sure is a very nice drum kit.
The answer at How to deal with people sending email incorrectly to my GMail account? confirms gmail doesn't differentiate between jharrop and j.harrop.
I assume ebay requires users to verify their address when they register. So I guess what has happened here is that the user subsequently changed his email address in eBay, and there is nothing there to require him to verify the change?
In eBay, the "Update your email address" dialog has a confirmation step:
Just one more step! We have sent an email to your address ... In the email message from us, click the "Confirm Email" link to confirm your email change.
and the address does not seem to change until you go through the confirm step.
So how did this guy manage to give eBay my gmail address?