In these situations I prepare defence tools
Defence 1.
At the consultation I enthusiastically say Trance or whatever genre it is and say that really worked picking a genre at Hollies wedding i did a really good Hour set of RNB then went into standard music for a wedding it worked really well and everyone was happy , this tries to focus there genre to a hour , if they insist on a whole night there is not much you can do except say no which i have done before now.
Defence 2.
At the consultation I ask if the music genre is on the invitations and all the guests know when they say no i say " Oh right" in a tone that makes them think lol
Defence tool 3.
I ask for a play list from both the groom and bride and print it out when people ask why you are playing this

I say the bride or groom specifically asked for these and your not going to spoil there special day are you? (see what i did lol turn it around and make them guilty lol)
Defence tool 4.
I Announce to the guests As this is such and such wedding they have specifically requested that there Disco reception be a little different, so tonight we are not having a standard cheesy wedding music its going to be ...TRANCE!! then kick off with a big tune. let them know the score from the off
Defence tool 5.
Send them to the Bride or Groom . At the consultation i say I understand this is what you want but you will have a lot of complaints from family and in my experience these can lead to people being offensive and rude especially when they have had a few to drinks If they are giving me
too much hassle is it all right to send them to you? This either leads them to change there stance on the music or gets them to say yes , if they are prepared to take the flack then fair enough i send them there way.
Defence 6.
I openly ask at the consultation that if i get over ten complaints from different people can i play other genres, I ask if I can play requests.
On the whole i have found that there are far more couples who are not considerate about other people. Yes its there day but they are taking it to extremes , a wedding is about showing everyone your commitment and love for each other not for force feeding your tastes of décor and music down every ones throats and stamping like a spoiled two year old if you don't get it your way.
I have turned down a few weddings because at the consultation I felt they were unreasonable people, for the ones that have fair reasonable demand i work my socks off for them.
absolutely no offence is meant to you marble but this couple if they are so much into trance why are they not hiring a DJ known in that field? I would say either its one doesn't exist who will do weddings in that area or the ones that are are WAY too expensive.
So they have made a choice on a recommendation of a friend, they
can't expect you to be Trance DJ of the year so may be you are putting too much pressure on yourself, there real expectations may not be as high as what you expect of yourself.
What i do know from reading on various forums is that you Marble are a great DJ and Host you have years of experience of dealing with often difficult situations and coming up smelling of roses and getting high praise from not only your clients but your peers , I feel you will find these Weddings much easier than you expected ,after all if we can deal with hen and stag parties full on booze fuelled 21sts a few guests moaning about song selection that is out of our hands is hardly the biggest challenge in comparison
I Hope it turns out great ..good luck and let us know how you get on
Rob