Would they be locals offering cruises at Zhejiang Wharf for people with not booked cruises?

I am afraid that there are no private cruises operated by locals from Zhujiang Wharf to Yangshuo. You may take an official cruise instead. The super luxury class costs CNY 450 or 380; the luxury class costs CNY 270 or 240; the ordinary class costs CNY 210 or 190.

You can ask your hotel to book the ticket for your, or just buy the ticket on the spot upon arrival. Don't worry! :)

I see, thanks for answering