There sure is allot of confusion about diving in Green Island. It is simple, if you don't speak Chinese it is going to be difficult for you to arrange something by yourself unless you use Blue Safari diving (
http://www.blue-safari.com.tw/index_en.htm) . If you are going on a week day anytime of year it may be difficult to do a boat dive with any of the 8 operators that have boats cause 1. the shops are usually closed mid week and 2. there is not enough people. Of course if you are going on a pre arranged group dive trip then it is no problem.
I personally use CF Diving (talk to 'Blackman') as they are the oldest outfit....I have brought at least 15 groups of divers to them over the past 3 years and have had no problem. I guide all the dives on my trips but know both of the brothers there are excellent guides....but they are not babysitters if you know what I mean.
About the sharks. There is only ONE operator that goes to the site where the sharks are. The rest of the operators dont want to have the responsibility cause it is a dangerous site. What is dangerous? Every year there are incidents (Death/s and or serious injury/s) at the site.
As far as Green Island Adventures goes...well I dont know or hear about this operator. I think its more of a middle man operation.