i agree with Dazmond, do a good job for them at a decent price then they cant complain about your work. If you do it as cheap as they want they want, you will rush it and cut corners at best, they will then complain that your work is crap and possibly give you a bad rep.
Dont fall for these people - no one will do 57 windows for £12.50 (unless i read that wrong) but anyway, no one will do an 8 bedroom house for £12.50 they are just trying it on to me - full of their own omportance the f%^$£*g arsoles.