Freelancers: how do you use Agile methodology in your client work?

Especially in terms of managing expectations and structuring iterations. When the client wants x product by a certain date, do you split it up into sprints and have the client pay for each iteration piecemeal as milestones?

How do you convince the V.P. of Engineering to follow agile practices and allow pair programming?

What tools do you use to achieve agile software development process?

I use trello. Lot of people use kanban. What do you use and why?

Why do you love Agile methodologies?

What are your reasons for loving Agile process? In other words, how has Agile helped you in day to day development?

Should Agile be followed at Startups?

As we know, Agile is a successful methodology in bigger organisations to organise how people work and interact with clients. Should it be also followed in newer startups? Looking for feedbacks.