The person asking the question will come to know whether the answer is correct or not by trying out and seeing the output. This is applicable to forums where the answer depends on the output.

I also partially agree with you on who will decide the Best Answer. For this I'd like to say that the top contributors will decide the best answer. You can set a point limit, like Stack Overflow. Only members above certain point level can decide best answer. The person who asked the question can only mark the post as Answered.

At present, the visitors have to watch and read each and every answer. If the question is marked "Answered", the visitor can immediately determine which answer was close enough.