Just a few rules when you are wwoofing  

Always make a arrengement with the host before coming.

Always tell the host if you change your plans, and don’t want to come anyway.

You can stay with the host for any period of time, but if no special agreement is made, limit your stay to 3 days.

Travelling as a wwoofer implies that you help the host with the work for at least 4 hours a day and furthermore participate in the general housework