Just make sure you are there when he does the job,had a chancer a few years ago who I specifically told to call at a time when I would be present,turned up cheekily when no one at home,sprinkled gutter debris around the house then reappeared when I got home looking for payment,told him he was a cheeky fellow and demanded he get the ladders so I could inspect his work,he said he would pop off home and would return in 30 minutes with them...
never saw him again.