As mentioned by ither users, the price on listing is determined by the project itself but its potential market price will then be determined by the demand a token will create in the eyes of investors. With regards on buying a coin after being listed, it will depend on the token itself. If it is really promising then ofcourse going at it would be a good idea but if not and only driven by the idea of missing the opportunity, then that would be a gamble already. Also with instances of buying when the price have already increased by huge percentage, you could be the liquidation of those who have bought early. Always manage the risk and gauge the tendencies from doing so.