I've got an iPhone 8 in fully working condition - the screen itself is flawless, having been under a protector for its whole life, but unfortunately the back glass is totally shattered.
Will Verizon accept this device for trade credit?
Not for the full value if they do. The back is worst since that isn't something you replace as easily.
It's always good to know what to expect when looking at a trade-in promotion or credit, so let's check that out. It is very good to know that the screen of your phone is good, and the phone itself works well. However, the backing of the phone would be considered physical damage to the device housing, meaning that will lower the value of the phone: https://www.verizonwireless.com/support/knowledge-base-141941/ . Just like @Tigerstep had mentioned, the backing of the phone is not something that can be easily replaced. If you have insurance on the phone, an insurance claim would not cover cosmetic damage, so I would suggest contacting the manufacturer to see what their repair costs would be: https://support.apple.com/repair . If the repair costs is less than what the full trade-in credit would be, then you'd benefit from getting that fixed. Does that help with what you wanted to know?