Is This A Defect Or Is It Normal?

I purchase the stamp and realized there is a tear on the stamp, asked seller about it and he said he said that is not a defect. this is the first stamp with grill that I purchase, I want to know if this is normal cause by grill?

No, it is not normal. The stamp is damaged, and it appears to be caused by hinge removal. I see the tear and it also looks to me as if the area below the tear is badly thinned. Either that or someone did a poor job of trying to seal the tear. This vastly lowers the value of the stamp to a tiny percentage of catalog value if anyone would buy it at all with so many sound copies available.

PS: The grill is completely irrelevant to the topic of the damage.