Using https://secure.sprintbuyback.com/cns/selector if you say your Nexus 5's carrier is Sprint, the trade in value is $97, saying it is T-Mobile, $150
And we all know that there is only one Nexus 5, Sprint and T-Mobile use the same exact model.
The site requires you to enter your phones serial number too after you select the phone, which makes this difference in pricing awk.