I want to add that there is also a third appeal process if the accused does not agree with the decision taken by the appeals committee. The third process involves the branch. The accused can then write a letter stating his case and the reason for disagreement to the Branch. The decision is then turned over to them.
Regarding the guidance of the holy spirit, you have to also add the human element. One example is Judas Iscariot. He was named with the guidance of the holy spirit to be an apostle. He was also guided as he ministered to Jesus, but he chose to not follow the guidance of the holy spirit when it came to treason. I will not sit here and say that mistakes are not made during judicial proceedings, but that is why there is three or four sitting on each judicial committee and why there is a an appeal process. This process might get mocked, but it works well in most decisions. I've been in judicial hearings were one of the elders wanted to disfellowship, and the other two reasoned with him that this would not be the right decision. They reasoned with their fellow elder by using the Bible and publications entitled "Determining weakness, wickedness, and repentance"