I Like You
I believe customer partners have two sets of motivations. For lack of fancy terms let's call them professional and personal motivations.
Appealing to professional motivations requires that your proposals help your clients perform their jobs better; ex. helping them meet their targets or deliver on their expected performance levels or look good to their bosses.
Connecting with personal motivations will have clients enjoying your company, looking forward to your calls, and trusting you with talk matters even outside of work. This is crucial but not easy as you have to be an authentic, consistent and non-opportunistic friend.
Tackle both effectively and you've got some cool deals coming your way!