No, he didn't do you a good turn. That Ellis was a more valuable bike. You should also probably punch him in the mouth for being a jerk and screwing you on that bike. Now he's taking you for a fool and trying to pass off two bikes he doesn't want and get 200 out of you. You'll pay for his Ellis and he'll have 50 to spare. This guy is screwing you. Keep your money, walk away, and keep looking elsewhere. You need to find someone near you who you can actually trust who knows about bikes. That or you need to slow down for a minute and do a lot of reading before jumping into another purchase. The Classic and Vintage forum here would be a good place to start. Just to put things into perspective some for you, I sold an Ellis-Briggs 531 frame, Just the frame, for $250. It was a little nicer than the bike you were looking at, but you get the point. I'd have trouble selling that Dawes hybrid for $100. That guy screwed you. Anyone who would go buy a bike out from under you is Not someone you should be trusting. Think about it.

Where in the U.K. are you? Link to your local CL? Maybe someone here will be nice enough to look around for you.