£35 for someone to whack the preload up to full for you is a f*ckin rip off.
Expect to pay far more than that to get it to work properly as you'll need lots of new parts.
However if that's a few meetings of "is it doing this here, does this happen when you do this" etc etc with a few tweaks in between on a fully adjustable bike that's reasonably well set up then £35 is reasonable.
I don't think a good setup can be established just from bouncing the bits and twiddling, it needs feedback from the rider and interpretation with knowledge. For my money you're better off learning this yourself.