OK, I figured this out. You have to be proactive. eBay doesn't appear to notify you about FedEx label adjustments. I have a few very slight adjustments, and never got a message or email about them. If you go into Orders -> Shipping labels, in the "Shipment details / Cost" column, you can click on the service name (like "FedEx Ground".) That brings up a popup with basic information. Click "Show more", and it will show the estimated cost based on the original weight and dimensions, and then the actual cost, weight, and dimensions. Note the estimated cost appears to be lumped together. The estimate has $0.00 listed for the fuel surcharges. If you see something like an estimated cost of $14.50, and the actual cost is $15.50 plus an actual fuel surcharge of $1.75 is listed, you were only adjusted $1.00. The $1.75 is included in the $15.50, and whatever the estimated fuel surcharge was, it was included in the $14.50 estimated cost.
Maybe there's a threshold, and I wasn't notified because the adjustments were less than $1 or something. I don't love wondering if there was a huge mistaken adjustment if most people just never know it happened. That would be pretty evil.
