I was fully aware of the horrible stories and one star reviews of the fajardo-culebra ferry on tripadvisor. One thing I can say is tripadvisor's review is so accurate and fully reflect the real situation.
I actually played a trick and came to the ticket booth one day ahead and there is a separate trailer not far away which sell advanced ferry ticket. I thought that I hit the jackpot because six persons in front of me all got their tickets to culebra! However, when it was my turn, the ticket man told me that he won't sell any tickets to me!
I asked him why he sold tickets to other passengers. I even had the passenger in front of me asked him in spanish. They had some heated exchange of words and the passgenger in front of me told me the ticket man was biased.
What can I say. My advise is you have to speak fluent spanish (do not speak english even if english is also official language) and look like local, and come to the booth one day ahead to make advanced purchase. And if possible, ask the passeger in front of you to buy ticket for you and you pay him/her in cash after she/he get ticket for you. that is probably the ONLY way.
This is discrimination in the worst way.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.