Occasionally we receive a request to certify a translation performed by a third party. The third party is sometimes the inquirer/prospective client, someone they know, or possibly even a machine translation output (possibly not identified as such).
Generally speaking if our company certifies a translation it means that we have followed a process that involves linguists who perform such services professionally for a living. We’re not sure what other companies do but this has been our policy.
So we respond politely to these inquiries but to this point in time have always declined to certify translations except for those we provide.