at a price lower than 10k the price of tc will go up no matter the kind of event,
higher than 10k and it would vary based on the status of the server and the kind of the event (in double exp/skill dominated/no war server generally tank prices above average, servers in war would vary a lot; in the otherhand while double loot events it will go up slightly or considerably but always up),
at 20k+ when double loot price goes up, when double skill it goes down.
anyway this "rule" vary from server to server but at least in GBE double loot event is always a good moment to sell TC, while double exp event depends on the conditions of such server and tc price but only new server with TC below 20k suddenly start raising the price until reach an "stable" price.