Who I have the same questioned this topic

TL;DR - Verizon screws you on the value of your existing phone if it's not purchased from Verizon

Used trade in program for 2 phones to get new iPhone 13's on the recent promo.

iPhone 11 purchased from Apple - trade in value $700.  Final credit $350.

iPhone SE purchased from Apple - trade in value $350. Final credit $200.

Both trade values decrease due to "Device carrier was different than expected." Both phones were purchased from Apple to use on Verizon and only activated on Verizon.  

Total reduction $450.  I would have never done the trade in with that expected value.  

I called multiple times and each time they said I would get a credit. The credit never appeared and called again.  Credit would be applied. Called a 4th time and the rep said I wouldn't get the credit despite the the prior reports I would.  

False advertisement from verizon.  I'm planning on switching carriers now.