Day 21 Ferry ticket or not - Cycle touring in southern Thailand

I ride 16km from Nai Yang Beach, Phuket, to Bang Rong Pier to buy a ferry ticket to Koh Yao Noi for the next day, however I'm told on arrival that they can't sell me a ticket in advance. That's at ticket office #1, but when I eventually discover ticket office #2, they see it differently and sell me a ticket, plus the price comes down by 50%