I trying get to Blackthorn City in Pokemon Soulsilver and Pokemon Heartgold, but I can't because a guy is there say I need to buy a rarecandy and I brought it. Now when I trying to go to to Blackthorn City after I brought he still there. What should I do please help me?

Ok that guy doesn't let you passed unless you have done everything up to where you are in the point of the game. So go back to goldenrod and make sure you have defeated team rocket and such and check other towns and cities as well

I early did it, I figuring it out on my own about three month later, but thank you for answer my question.