If there is a crack on the back of my iPhone XR, will it still be able to be traded in?

You will need to reveal any damage while using this process; most likely, you will be offered to have the device recycled. Damaged items are usually not eligible.

https://www.apple.com/shop/trade-in

Julesbattiato Said:

"Trade ins: If there is a crack on the back of my phone, will it still be able to be traded in for a same value if it wasn't."

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Ask Apple:

These are User-to-User forums. We are not Apple. We are just everyday open-ended Apple users, such as your self. So, ask Apple, as they would have the answer for you.

So, Contact Apple Support:

Phone Support Info:

• Contact Us - Choose Locations
• USA: 1(800)MY-APPLE
• Speak with: Apple Store Staff
• Proceed from there as Necessary

Screensharing with the Apple Rep:

To easily show this to Apple Support, use screenshaing of another iPhone or your Mac. That will allow the Apple Rep to see this from your perspective. Ask a friend, or family member if you may use their phone, if you do not have a second device handy.

Learn more at these links: 

• iPhone: Screenshare your iPhone with the Camera App Enabled to Easily Converse Over-the-Phone with Apple Support - User Tips
• Mac: Screensharing MacOS FaceTime to Easily Converse Over-the-Phone with Apple Support - User Tips

For Note:

Why Calls are a Bit of a Wait:

Phone calls are taking a bit to go through at the moment, due to lots of calls. And, that makes sense because with the Coronavirus Pandemic, many are at home at the moment, with much time on their hands to contact Apple Support. So, just stay on the line, and you will get through :)