To clarify the rules on resisting Presence: One must spend 1 Willpower for each success, just as is true of Dominate. Partial expenditures will have no effect. 

For a Mortal / Mortal+ to have the option of spending Willpower to resist Dominate or Presence, the PC must either be set Vampire AWARE or have at least 4 dots in Occult. Also, if the PC has been affected by the Discipline on several occasions (4 or more). the Storyteller may choose to give them  the option.