Just wanted to give a heads up here.
I recently booked a gel manicure and realised the next day (a Saturday) after I'd booked it that it was the wrong day, my fault! I didn't realise until the next day. As I was in the area on the next day (Saturday) I rang the salon to ask if they could fit me in later in the afternoon. Yes was the answer, no problem. The manicurist did say she'd tried to ring me on the day when I didn't turn up and I showed her my phone and said you didn't ring on this number as no calls or missed calls there from hers nor on my house phone as same.
I had a good manicure but then when it was finished, they asked for cash payment - as it was late in the day I went to a cash machine to pay them but I realised that for a previous appointment that day with different salon, brows, I had paid via Treatwell automatically on my bank card. I still paid them cash as I didn't want bad feeling and didn't know if there was a mix up or not. Their card machine also wasn't working.
Later on I checked my Paypal account and realised that yes I had paid via Treatwell. I was quite annoyed to realise I'd been charged twice for this service so opened a complaint via Paypal. Found out today I got my all money back for the one manicure so I'm pleased. I actually wrote on my resolution that I didn't expect not to pay a cancellation fee but I didn't like paying the full price.
So if anyone else has issues like this I'd say definitely challenge it.