I think most of the exchange sites right now has their own bot but the bot is not a bot for volume it is a trading bot but if you are talking about the volume they can customize the volume through API to send in coinmarketcap almost all exchanges have fake volume according to some article that I heard before. Only binance have no fake volume according to that article(Sorry I forgot where I found them but it has a good analysis and exchange graph if where are big fake and low volumes.).