I suggest you tell your friend to walk away from client that asks for this kind of service. Although possible it is considered unethical. Better to try to beat their rankings by doing a better on your own rankings.

SEO has really evolved over the years and will continue to revolve. One of the most important aspects of SEO is back-linking. This alone has the most weight…but it's a good idea and best practice to do all other elements like meta tags, on page content optimization, unique relevant content…etc.