You asked a person to go and purchase a certain goat from a certain person for R200. This wakeel cannot go and purchase that goat at that price for himself. In other words, when you ask the wakeel to purchase something specifically for you, it is not permissible for him to purchase that very item for himself. However, if he purchases it at a price more than what you had specified, it will be permissible for him to purchase it for himself. But if you did not specify any price, it will in no way be permissible for him to purchase it for himself.
You did not specify any particular goat. You merely asked him to purchase a goat for you. It will be permissible for him to purchase a goat for himself as well. He can purchase whichever one he wishes to purchase for himself, and whichever one he wishes for you. If he purchases it with the intention that he is purchasing it for himself, it will be his. If he purchases it with the intention that he is purchasing it for you, it will be yours. And if he purchases it with your money, it will be yours irrespective of what intention he makes when purchasing it.
He purchased a goat for you. However, before he could give it to you, it died or got stolen. In such a case, you will have to give him the money for that goat. If you tell him that he had purchased that goat for himself, then your money will be lost if you had already given him the money. But if you hadn’t given him the money and he comes to you now to ask for the money, then if you are able to take an oath that he had purchased the goat for himself, then his goat will be lost. And if you are unable to take an oath, you will have to accept his word.