Buyer claimed I sent them an open product MTG TCG product missing booster packs

I sell low volume and source MTG products directly from authorized distributors. I personally inspect and package every order and do not resell returns.

A buyer purchased a sealed MTG bundle, then opened a return claiming the box was opened and not in original packaging and all the booster packs were missing. This is the first time I’ve received a claim of this nature.

I sell at a very low volume and personally package all orders so I definitely would not have sent an opened product that was missing the booster packages.

I ended up already authorizing the return and provided them with the shipping label to send the product back. I checked the tracking and the buyer has already sent it back and I’m expecting to receive the return box next week. Based on everything the buyer is saying, I fully expect the item to come back opened and missing boosters.

My frustration is that missing booster packs destroys the entire value of a sealed MTG bundle, yet the return process appears to require at least a partial refund even if the returned item is materially different and no longer resellable as a collectible. I’m also not accusing the buyer of anything but it seems there’s really something fishy going on with their claim.

From what I can tell, my only option if the item is returned incomplete is to apply a maximum 50% deduction, even though the product is effectively worthless without the boosters.

For other sellers that have been through something like this, what did you end up doing and what was the outcome? Am I able to do a 100% deduction as the product is effectively worthless? What about the buyer’s claim that I sent them the product like this? How do I fight it?