No, the question was this one: does the electrician actually base his calculations on a common method or is this fraud?
And now let's ask ourselves together, which audience this question was probably addressed to:
a) electricians who regularly disclose their calculations in this forum
b) clients who have dealt at least once in their life with one or more electricians and can take a look at the invoice or their offers from back then
This has nothing to do with the assumption,
that the client does not want to recognize an entrepreneur in a craftsman
but rather with transparency and business conduct.
It may be that in this case it is really a poor craftsman who is being exploited by his general contractor. But is that really the OP’s problem? Does the electrician even need to do that in the current market environment? Especially since the solution to this dilemma is so obvious that you already presented it to the OP 20 minutes after his initial post.
Anyone who calculates as an "entrepreneur" in such a way that he has to squeeze disproportionately much money out of uninformed laypeople in a bind (signed GC contract) for extras in order to survive, in my opinion not only acts quite antisocially, but also runs the risk of being ruined within a very short time as soon as 2-3 clients in a row question the pricing policy and react accordingly.