AFAICS, everyone involved acknowledges that that is what is going on. Different people will have different views as to whether that withholding is reasonable and/or justified.If the electrician fears damaging his relationship then he clearly fears that the builder is indeed withholding the certificate in furtherance of his dispute.
If I believed that a client owed me money in relation to a project and I had subcontracted some of the work (and quite probably already paid for it), I probably wouldn't hand over the work done by that subcontractor until the dispute had been resolved.
Kind Regards, John