Basically, the hidden charge as they justify it "for a toner" was almost the same price as the voucher, which I felt was totally unreasonable. When I arrived to the salon, they informed me that the extra charge will be £30 at least (even tough my hair is long, the highlights needed only to top up the work that's already been done about 5-6 months ago), I felt totally surprised and asked to speak to a manager. The manager was in a different salon, and they kept me there for more than an hour until they actually got through to him. When finally speaking to the manager and explaining my frustration, he said I better come to his salon and he would be willing to "see what he can do for me". I had a baby on me, so we traveled for about 40 mins to Hammersmith salon, where he greeted me and said that he would be willing to reduce the price to £20. By then I would have already lost 2 hours of my time and spent some money on the journey to get there, so it came up to almost the same amount anyway. I asked Groupon if it was reasonable for the salon to charge that much extra (which to me felt more like a hidden cost), but the answer I got was: "it says from £10 so could be anything". Well, they don't say this on the phone when booking an appointment, and with similar deals in the past I used to pay up to £15 max, so this was a total surprise to me! Anyway, it was actually my birthday, so this experience made it more stressful as I had to rush back to a restaurant where a table was reserved, so I could great my guests when they arrived. Even though I did get a good haircut in the end, I just wish I was warned in advance, so I could make my choice according to my budget and not be hit by such a stressful "surprise" on the day.