Standards
Some ergonomists dedicate their careers to ensuring that companies comply with regulatory standards. The standards they encourage are often derived from the field research and insight discovered and validated through the user testing of fellow ergonomists.
For example: In the Canadian province of Ontario, it is legally required under the Occupational Health & Safety Act (OSHA), that employers respond to the recommendations made by health & safety experts within 3 weeks, and must further make plans to either implement them or justify their refusal to implement them. [OHSA, section 3, articles 12 & 13]
These standards, which are applicable in both usability and ergonomics are catalogued in the International Standards Organization 9241 (ISO9241): "Ergonomics of Human System Interaction" help guide ergonomists and usability professionals towards making correct recommendations, and can in turn protect or condemn a professional who adheres to or ignores them.
Guidelines
To give one more level of protection to clients and avoid poor recommendations & analyses, major organizations have established industry guidelines. These guidelines can be implemented by modeling assessments on prototypical studies (e.g. some students are taught to emulate Nielsen/Norman's usability report on flash applications), and by installing well-experienced experts in universities that produce new professionals. However, the most effective way to impose industry guidelines is through certification. Nothing can ensure that a client is getting proper service better than the accumulated experience and education required to be certified.
