Was Danny Wilson lying when he said on the 28th June "We haven't received any offers for anybody":-
http://www.sufc.co.uk/page/Gaffersnotes/0,,10418~2824523,00.html
I believe he wasn't lying which suggests that the first offer came in between the 29th June and 6th July.
7 days is hardly a protracted negotiation period.
Other clubs successfully use the media to play rival bidders off against each other.
They make it known that a bid has been received but is nowhere near enough etc..
Even if it's not the case, United APPEAR to accept the first bid because one day it's a rumour and the very next day the deal has been done. Naughton, Walker, Slew, Lowton et al...