I am looking for information, from reasonably credible 3rd party
sources, about reduced commission fees (%) paid to estate agents
(="letting agents" when they let instead of sell property) in north
London, UK.

This information is for comparison against my 3 bedroom house in
Belsize Park, near Hampstead Heath, London.  Information for a 1
bedroom flat in Wales (for example) would not be very helpful.

I already have several of the top agencies 'official' rates (between
10-12% for finding a tenant and an add'l 5-7% for managing the
property).

Basically I want to talk them down from these crazy prices and need
better market information.  I need something within the last 3 years,
the more recent the better.

Could be a challenge for someone familiar with discussion/ chat
boards.  I have looked on industry sites, but no luck.

'Reasonably credible' means that it was not obviously posted by the
agent themselves or by someone with an ulterior motive.

Many thanks.