How: instead of asking someone to fill out a form on your website to be contacted by your sales team, you direct them straight into Messenger, where you can ask them some of their contact details and any qualification questions (for example, "How many employees does your company have?"). Depending on what they respond with you could ask if they'd like to arrange a meeting with a salesperson right there and then.
From any point in the conversation, the bot needs to know where to go next. If a user writes, “I’m looking for new pants,” the bot might ask, “For a man or woman?” The user may type, “For a woman.” Does the bot then ask about size, style, brand, or color? What if one of those modifiers was already specified in the query? The possibilities are endless, and every one of them has to be mapped with rules.
There is no one right answer to this question, as the best solution will depend upon the specifics of your scenario and how the user would reasonably expect the bot to respond. However, as your conversation complexity increases dialogs become harder to manage. For complex branchings situations, it may be easier to create your own flow of control logic to keep track of your user's conversation.
ELIZA's key method of operation (copied by chatbot designers ever since) involves the recognition of clue words or phrases in the input, and the output of corresponding pre-prepared or pre-programmed responses that can move the conversation forward in an apparently meaningful way (e.g. by responding to any input that contains the word 'MOTHER' with 'TELL ME MORE ABOUT YOUR FAMILY'). Thus an illusion of understanding is generated, even though the processing involved has been merely superficial. ELIZA showed that such an illusion is surprisingly easy to generate, because human judges are so ready to give the benefit of the doubt when conversational responses are capable of being interpreted as "intelligent".