I hope this question makes sense... 
We went to see a house today, and the (apparent?!) vendor said something in passing that made me curious... They have reserved a new-build house which is due to be finished in the summer, and the house we viewed has been (or will be?) used as part-exchange for that purchase. So I've just started wondering... Who is actually the vendor - the couple living in the house, or the development company building the house they're buying who are taking this house as part exchange? And who will decide what offer to accept?
I think it's likely to affect negotiations, but I'm not sure exactly how! Does anyone have any experience or knowledge of this type of situation, please?