show a demo bot that is close to the bot they want. Let them pay half the money because after your done building the bot, most of them say sorry; I found a guy for cheaper or something dumb like that. After you build the bot show it to them then ask them what they want to change on the bot and make sure to take notes. After your done with the meeting fix all the issues he has with the bot wait 1 day so that he thinks the fixes are difficult and he will respect you. And then show the bot again, and if he is fine with it tell him to pay the other half and done...