Like many of you, I contacted a couple of tour guides as recommended by people in the forum. In the end, I decided to go with Catherine Lu (firstname.lastname@example.org). Please stay away from her.
She was not able to accompany us on our trip and sent her father instead. Mr. Lu is an dishonest and bad tempered man. The negotiated deal included toll, fuel and parking fees. At the toll booth, he said he had no small change on him and we ended up paying for the toll fee. He would park his vehicle so far away from the attraction to avoid paying for parking and we would have to walk a long distance. In the end, he refused to take us back to the hotel unless we pay him extra money.
Therefore, please beware and avoid going with Catherine or her father. Their vehicle registration number is PW 9152.