In my experience, Mugen waited until I was actually expecting to receive the cover, THEN I finally received a message saying that they only sold that item to customers and essentially asked me for an invoice or other proof.

At first I couldn't come up with proof, and reported that here. I had bought the big battery from them, so I thought they should know I was their legit customer, but they didn't.

But eventually I remembered I had made the purchase with PayPal, and did find proof.

I sent that to them, they apologized and completed the order.

I also complained a lot. I hope that they have realised that selling things is good, not bad, but I doubt it.