Undue influence is the substituion of one person's will for the true desires of another. Unlike common persuasion and sale techniques, fraud, duress, threats, or other deceits are often features of undue influence.
Quinn, Mary Joy
"Friendly Peruasion, Good Salesmanship, or Undue Influence,"
Marquette Elder's Advisor: Vol. 2
, Article 8.
Available at: http://scholarship.law.marquette.edu/elders/vol2/iss4/8