All non stores get 40 free listings a month, so you aren't one of the lucky ones.

A lot of us now don't do cancellations, we go the unpaid item route. Even if they ask nicely, I reply nicely that a case will be opened and they are to ignore it and to also ignore any automated requests to pay. Once the case is closed, it's all taken care of. I don't tell them they'll get a strike. Of course if they've already paid it's a different story.

If you go the UPI route, they can't leave bad feedback. If they do, eBay will remove it when the dispute is closed. I always use the term case rather than dispute as it sounds less threatening to the numpty (or their toddler, or cat, or pidgeon, or neighbours brothers wifes auntys sister in laws overseas sister who just happened to be on their computer).