Depends how badly you want it and how easy it is to replace for the price you paid.
When i bought a phone on Amazon, same thing happened. Now just see how sneaky this was. The seal was not broken. But you could tell the box had been tampered with and the phone taken out, and inserted back in. Cloudtail seller as well which is just some consortium of sellers around the country.
After examining the phone i found there was nothing wrong with it. No cosmetic damage. Some firmware checks all passed. It was a colour i wanted. I got it for 5k less than otherwise i would have paid.
I kept the phone and all is well. This happened one and a half year ago.
Well if you shot the unboxing video etc. you can very well claim and mention about the seal and get a new replacement. Else if only the box seal was broken but the main component is brand new/untouched then I dont see any reason for getting any replacement as you will have to devote few days or weeks time to investigate as all that stuff will go through checks etc.
I had ordered a Dell wireless keyboard from Amazon. The product came shoddily packed and the seal was broken and they had put a cello tape on the broken seal. I returned the product immediately (the delivery guy was still standing). I called informed them of the same made the delivery guy speak to the cc executive confirming that the product has not been accepted. They started processing the refund. I got the refund in a few days.