dont pay up front, you'll only regret it in the long run, especially if they tell you your money is spent and you 'aint ready for final handling test. Just one word of advice from an old hand, and that is in my experience 4 week PPL's are a bloody danderous thing. no time to assimilate the new knowledge you are aquiring, and I know a guy who despite being absolutely dedicated took a further two years to gain enough confidence to fly alone in the UK. probably extreme, but he is not the only quick built PPL I've had the pleasure of helping in one way or another.
Good luck and dont forget some people only run flying schools because they were crap at selling second hand cars.