Well other forums and their members/content are off topic here, so neither here nor there. The terms are just meaningless marketing fluff, but a straightforward 'expensive' is fine, since that's all it's describing.
If you're talking about Central London outcalls on a limited basis (and AFAIK this is a regular enough agency rate, but that's without the pimp cut which would likely be £100 or so) and assuming you have some reputation to come back to, then I don't think £300 is particularly pie in the sky. My outcall rate is a little over 2/3 of that although I do very few, and most are longer as I have a minimum duration for anywhere outside my immediate area - maybe do that too?
The only way to know is try - if you're turning work down then put rates up, if you get nish, then drop them