This sort of direct marketing is now becoming the norm for these sorts of Events, they often start the letter with "You have been recommended to us", or "As a professional Entertainer we would like you to attend", all this is corporate B/S for "We've got your details from a directory", so don't be flattered, or feel obligated to attend

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I have attended many of these over the years, but I've never paid more than £40, and that was for a 2 day event at a local hotel. I would NEVER pay £200 - £300 to attend.
On average I get around 8 - 10 enquiries from each event, around the same as I get per fortnight from my website!, which puts it all into prospective - especially if you are considering paying hundred's of pounds for the privilidge!.
What you may like to ask the organisers, is whether you are the only disco in attendance, if you are 1 of 10 roadshows attending, (and it is highly unlikely that you are the only one sent that letter!), then you are not even getting sole service representation for your money which makes the chance of getting booked even slimmer!.
I've also found when I've attended the event, that they automatically assume that I will allow them the use of my P.A for announcements and music for the Fashion show

. I always agree - providing that they pay the hire fee, which by some strange coincidence is also the same as the attendance fee.