Most TO's work on a 60/40 ratio.
That being 60% of your total holiday cost for your flight, 40% for accomodation, transfers and reps service.
So for example if you are in a shocking accomodation with many legitimate complaints you can fairly ask for 40% of your total holiday cost back.
Wether they will give it without a fight is another matter.
A TO will rarely offer to recompense the whole holiday unless it is taken all the way to court/arbitration. I doubt a judge would look favourably on the 60/40 so worth a go if the complaint is strong.
There are some members here who have received the whole amount back plus some extra who can advise better than me.
Louby