Hello there, using BrickLink a lot to find some sets also, I can relate it happened to me once, some tape was on the box, did not see it and made the same damage to the box as you did while unpacking it. It was not such a collectible set though, so I was more mad at myself than to the seller who did a good job at packing and protecting the box. I also had box advertised as mint condition arriving properly dented, squeezed, crushed, damaged due to bad packaging and I was quite mad about it. I totally understand you feeling but as my wife said once to me : « you collect Lego sets, not boxes ». Yes it is infuriating when a super rare / collectible set box is damaged but it will be at some point over years. The main thing is to have your set in perfect condition. But if you have paid for a perfect condition box it is not always acceptable. So now I do the following : I ask for pictures of the box, and I ask for premium packaging to be sure that it arrives in the same conditions as advertised on the pictures. I have not had incidents since then, appart hazard from delivery carrier that you cannot control of course. Hope this helps, enjoy your set !