I cracked a basin once,when tightening taps,hot I think,I was just applying the final twist when my tap spanner slipped and my knuckles went crashing against the wall,recoiling from the pain,I raised up and hit my head against the basin,which made me twist and fall against the w/c pan,the painter at the time had a short scaffold board on the pan across to the bath while painting the ceiling,this i knocked and set painter flying,his white apple tinted matt emulsion paint for kitchens and bathrooms tin flew through the air and caught the edge of the basin, causing little chip,apart from that never seen tap tightening cause any damage
As for who pays,obviously in this case it was the painter,after all it was his paint can 😛