99 times out off 100...  you both show up, you put the donation in plain view...  proceed from there.   The only RARE exception is where somebody richer than me flys in a gal he can't live without...  she would likely require enough to cover her travel expenses in advance.  Such situations ussually involve person who have met previously...  often more than once...   If experienced hobbiests break these rules on occasion...  they know the risks they are taking...  
H