Check genuine tradesemen

Hello, I am about to hire electricians for a Rewiring work. I have found them through RatedPeople website. They are registered on various websites: RatedPeople, MyBuilder, Checkatrade etc They claim to be Elecsa register d and they supplied the respective registration number. Is this sufficient to assume they are genuine? What can one do to be (almost) certain this is not a con? Please note that I have not got any reason to beleive they are not genuine, after I have met them. Many thanks Vladimir