Used device buying website UpgradeSwap said that it will “never buy back used T-Mobile devices again”, as a result of the US number four operator’s new approach to device financing.

The company said that T-Mobile US has a “unique (to put it nicely) approach to IMEI checking”, which means that potential buyers of new devices are told if a device is not blocked, but not if it is still subject to financing – “because they aren’t allowed to”.

While that makes sense for customer privacy reasons, it means that if the original owner stops paying for the device after it is sold, T-Mobile would then block the IMEI – even though it has now passed to a new owner, who purchased it legitimately.

UpgradeSwap said that, in contrast, AT&T, Verizon and Sprint will tell potential buyers if a device IMEI is still related to an active account, which could lead to potential issues if the original owner stops paying.

“T-Mobile won’t tell you if it’s active and that’s a big issue,” it wrote.

In response, T-Mobile told BGR that potential buyers of its devices should use its own IMEI search tool to check the status of devices, although it is not clear how this resolves the issue of device owners stopping finance payments after offloading the handset.

T-Mobile US was the first operator in the country to split-out handset subsidies from service plans, enabling customers to trade-in handsets at any time. This model has also been adopted by other operators worldwide, who are looking to reduce handset subsidies in the face of spiralling smartphone costs.

While subsidies provide a way to make more high-end devices available to customers at more affordable prices, the related uptick in spending on mobile data services is less pronounced, impacting operator margins.