Can I sell full Warframes?

Excuse me, I was wondering if I could clarify something about Warframes. Is it possible to sell entire Warframes, or are they strictly for use and customization within the game? I'm just curious as I've seen some people discussing trading Warframes and I'm unsure if that's actually a feature available within the game. Could you please shed some light on this matter? Thank you in advance for your assistance.