Yes, there is a big difference between 25 and 70$. If you were just starting out a killer of a difference. Personally, I can see why you'd want, to cancel, of course. If you asked the buyer, and explained why, and they were OK with it...I can't see why eBay can't remove the defect.

If the buyer was happy to contact eBay and say they were 100% happy with ending the sale.

Personally, I'd have thought, ugly cost but I'll honour it. I wouldn't like it! But ... I'd feel the buyer wasn't at fault, either ... After ten years here, and being treated well by most sellers, some who did fantastic things.

New...I'd be very unhappy and confused and not know what to do. Like the OP.

I get that the eBay defects system has little leeway for error.

IF a buyer is fine with how some change (not just a cancel, but any change) to the deal has gone, then eBay should factor that in though. Like they allow revision of a negative.