Once a bid is placed on the card, the seller CANNOT change anything about the listing. The only thing that they can do is append the description (which is obvious to see), but everything original will be there as it's locked by eBay when the user should go and try to make any edit. I think in this case, you must have missed the "Poor" comment.
Not uncommon, but not the best practice by sellers. If it's someone who doesnt frequently sell on eBay, they probably would only check the site once they know all their items have sold and even then, they aren't in a rush. Customer service obviously isn't their #1 concern.
If I recall, this is actually the eBay default. Some users change their setting to send an invoice immediately, some after 1 day, and some even, say, a week.
Yes, you are obligated to buy it. You bid on the item knowing that there wasnt a back scan. Just because there wasnt and you missed part of the overall description, and they were slow to respond to your messages (which they technically arent obligated to do), does not mean you aren't contractually obligated to complete the transaction by paying for it.
We've all done this before, myself included (multiple times).
Pay for the item and consider it a very cheap $11 lesson.
In the future, either ask for the back scan before bidding, or just know that you are taking a risk. Most users on this site either demand a back scan or just skip the auction entirely.
Hope this helps
