I would take it at that price. Just make sure it includes any issues that may arise following the installation. Get that in writing. If he doesn't give you it writing then he is in breach of the law and the rules of his competent persons scheme.re it being safe. no checks were made , he just said it was old CU and needed updating and he would do it for 200 plus cost of new unit. He is part p reg so presumably knows what he is doing
If he is willing to take the job on without any prior checking of the circuits then the risk falls on him to ensure everything is up to current testing standard. I would never ever change a board without completing an EICR.
If he says he is 'part p' whatever that means check that he is registered with a competent persons scheme something like NAPIT or NICIEC or several of the others here:
http://www.competentperson.co.uk/