If the electrician has performed general electrical work then a COC is mandatory and must be completed by the electrician who did the work. Other than the time it takes to complete you shouldn't really be paying anything extra for a COC as all the testing required is also mandatory. I understand some electricians will charge as every little bit of income helps.
I agree. As it is mandatory then it is part of the labour content of doing the job & should not be an added on charge. It's double dipping in my eyes.
A COC is not mandatory on every job, and Electrical Safety Certificate (ESC) is. Considering they are both legal documents $20-$35 is a reasonable cost seen they have to be stored and produced on demand for up to 7 years. A lawyer would happily charge to produce a legal document and people wouldn't say anything.