I blundered in rather naively, not considering club going bust etc, and paid a club half of a PPL instalment, followed by 2nd half after 22 hours. This was after 3 trial flights in different schools. The club has been going for 80 years and had a "good feel" about it. The first place I went to had a deal where you could pay all upfront but had to guarantee to complete in 6 months! I walked away... The school I ended up in gave me a guarantee of fixed prices despite AVGAS increases, and, in the end, threw in an inclusive night rating.
I found that not having to pay each time hugely increased my enjoyment, and not thinking "there's another tenner" after each touch & go helps greatly! It saved me money in the end, an I completed my ppl much faster than I otherwise would have (which, of course, will end up costing me more money!) I am not denying there are risks, but it worked out well for me. Do consider trying 3 or 4 trial lessons with different clubs & write off the cost the way you would a house survey - it will save you the money in the long term! You will get a good feel for the club which works for you.