I would never do such a thing
, I have a very good personality. I even have done some work not included in price agreement for free... I installed few pendant and wall lights and fixed some serious electrical issues which were not a problem with older customer unit but after replacement didnt work. I had to change a cable from fuse box to the kitchen and didnt say anything: /
I also fixed broken cable in ceiling which joiners have destroyed whilst doing its renovation. I think she is very lucky I had a camera which I put through the hole and I was able to find a box so with almost 0dmg I fixed the light. Most electricians would just pull out cable from pendant, brake everything and tell her to renew ceiling from scratch.
she agreed to the final price at the very beginning, I havent added anything, even though I have done big surplus work.