If one follows the Form 5500 Instructions for an authorized service provider’s signature, that signer is not responsible for the Form 5500 report; rather, one signs only five process statements about how the plan administrator’s signer authorized the service provider to submit the administrator’s report.
If you do something else, consider that the signer states:
Under penalties of perjury and other penalties set forth in the instructions, I declare that I have examined this return/report, including accompanying schedules, statements and attachments, as well as the electronic version of this return/report, and to the best of my knowledge and belief, it is true, correct, and complete.