Sadly there is no official accreditation, which does make it easy for any Tom, Dick or Harry to setup as a "data recovery expert".
We get 90% of our business from repeat business or recommendation.
As far as legal backup goes, there nothing specific as far as I know. But as mr_spokk says NDA's are sometimes required which we don't have a problem with signing.
The police and other government bodies trust us with their data and our premises and facilities have been inspected and approved.
With good results and professional service comes trust

If you wanna chat, gimme a buzz!