It is a very confusing process. I, too, didn't realize that there was a reoccurring monthly fee.
I'm pretty careful with agreements, so I don't know how it slipped past me.
Even the cancellation process is kind of weird. You don't cancel the sellers account; you remove your payment information. It is strange to cancel an account by basically saying "I'm not paying you anymore."
http://pages.ebay.ca/help/account/closing-account.html#seller
'My eBay' (top corner)
'Account' tab
'Seller Account' (left column)
under 'Payment methods for Seller Fees' click 'Remove automatic payment'
Remove your payment info (Notice that it says you will lose your ability to sell)
Now, another thing is that even though you aren't selling anything, you can still have a 'store subscription'. If you also have an eBay store:
'My eBay' (top corner)
'Account' tab
'Subscriptions'
Under Active subscriptions, find the eBay Stores subscription and click either Change Level or Cancel Subscription
If you have bundled subscriptions with your eBay Store (for example, Selling Manager or another selling tool), select the appropriate option to specify whether you want to keep the subscriptions at the new monthly fee or unsubscribe.
If you are sure you want to cancel your eBay Stores subscription, click the Close store button.
