Wouldn’t it be better to have the users fill out the title field and use it as the client name? Woothemes’ testimonials plugin does this. If that’s not an option, you can look into adding a filter on title_save_pre. Haven’t used it myself but here are examples:
- From StackExchange: Title_save_pre – Simple problem that u know for sure
- From WP Support Forums: Generating and setting a custom post title