tonyh29: To attempt to reply for the general....
The difference between Villa's situation and your example is that the chance you and the person you purchased your house from doing another deal in the near future is small, thus the fact you (presumably) overpaid for your house doesn't matter, that and the fact you wont buy another house soon.
If we bought Bentley for say £25million (a price most would agree is a bad deal for us) from Blackburn, even if he is a great success on the pitch we've permanently weakened our negotiating position. In the future if we go to buy a player the club will presume we have money to spare and force the price up(even only by a small amount, if it happens repeatedly it adds up). Such as the situation with Chelsea buying Bosingwa, I doubt as a fullback hes worth 17million but as everyone knows Chelsea are rich they've been forced to pay it. The issue is that Chelsea are rich and they can afford it, we can't afford that to happen on a permanent basis.
One of the key points in negotiating is to have a strong starting position, and ensure the person on the other end of the negotiating table knows that, having alternatives and not conceding on price too easily is one of the best ways to do this. Similar to the way Rafa has sent about 3/4 slightly higher bids to us about Barry in a short period, hes made himself look very weak and desperate especially as he doesn't appear to have any alternatives lined up.
Its frustrating but its the best long term policy!