Any cellphone carrier (US) that has right of phone sale?

I’d like to update my smartphone (Android 2.2, have had it roughly 3 years), but I don’t need the latest gizmo. I’d be perfectly happy with last year’s Galaxy S3, but my carrier pretty much makes buying a used phone impossible.

I bought a private-refurbed phone, the seller claimed that the IMEI was clean, but when it arrived, I couldn’t connect to the network because the IMEI was flagged as lost/stolen. Fortunately the seller had a good return policy and I got my money back. (AFAICT nothing would have prevented me from buying a used phone, successfully using it for weeks or months and then suddenly have it flagged.)

But this incident made me realize that (at least with this carrier) if I ever wanted to sell my phone, there’s no way I could contact them and say “this is no longer my phone, don’t allow me to flag the IMEI” so that I could sell it with no strings attached. If I can’t sell it, I don’t own it, I’m only renting.

Does any US carrier have a system by which I can be sure when buying a used phone I can claim it as clean and not have to worry about the IMEI later being flagged?