Is there no place in the game to sell power frames? If not why?

Arms dealer in Goodneighbour does, as does the Brotherhood of Steel merchant. These are the ones I know about but I don't wear power armour so I really haven't paid attention to which merchants sell it so there could very well be many more.

They cost 1000 and they are listed under misc I believe.

It looks like he is trying to sell off excess power frames, rather than buy them.
I have not seen any way to do that in game to be honest.
I have seen those power frames listed as NPCs in FO4edit though.

Tea I got like 8 of them just sitting in my Red Rocket junk yard it would be great to sell them and get some radaway.

Why sell them when you can create your very own army of remote controlled Power Armors. They are more customizable and very likely more common than Sentry Bots and Assaultrons.

Is that true? you can make remote controlled power armor?

......this would be the first time I've heard of remote controlled power armor.