How can I measure Social Media Marketing

I am from India and we are extremely money conscious. Oh, it's true. It's damn true. Not that it is a bad thing. On the contrary, it means you value your money. However, when it comes to selling your brand or your product it could test your wits. If you have gone selling your brand or product to a prospective client you know what I mean. A good salesperson will always ask himself or herself the same questions the client would. Like, "How much business will I get in return?" or "How can I know I got business from online marketing?" So how do we answer these questions? ...