From what I've gathered in my research, Foxton's a) will say "sure thing", then proceed to show you flats far and away over your budget, presuming you'll just give in and pay it, I suppose; and b) there's a general consensus that a flat listed by them is too often overpriced and they're not as willing as other agencies to negotiate it down to more reasonable market value.
FYI, Foxton's was briefly in the US but went bankrupt in short order (well before the financial crisis). Something about their business tactics not working well in this environment, as I was recall. And that was even before the founder sold it. Go figure.