Link building is the gold mine for SEO. Even with the numerous changes to the search engines algorithms, it has remained an important search engine optimization strategy. This is because SEO link building provides two main advantages. First, it provides a source for direct organic traffic to your site. Secondly, it allows you to rank higher in the search engine results by passing authority to your site.
Considering all the advantages that SEO has to provide a business, you need to present these advantages and justify the money the customer is paying.
The most tried and true way is to request links.