Having read both posts I would have to say mistakes have been made on both fronts. Anytime I do work or have contractors in my house I will happy sort out a deposit for materials before starting, the rest is paid on satisfactory completion, this way both parties know where they stand.
From the pictures it is clear that the guy has made a few mistakes, which with a bit of work can be remidied (basically addressing the 4th wall which is a long way out) Once the work is complete the guy gets his £'s.
There is a thing out there called "reasuringly expensive", basically meaning that if you have bought some nice tiles and want a flawless finnish you have got to pay the going rate (think M&S advetisements!) If you pay a very low rate then you have to realise that the quality may suffer as a result.
First thing first is you need to talk to each-other and reach a compromise.
cjbombero