I reserved a room in Florida for a week. I didn’t give a deposit because they trusted me. Now because of a simcha in the family we cannot go. What am I responsible for? Minhadin and/or lutzeis yedei shumaim?
You are exempt from payment.
Generally one is obligated to keep to his word, even without a halachic acquisition. One who backs out is called “mechusar amanah” an untrustworthy person. However, when new circumstances arise which force you to back out so as not to sustain a loss, your actions are not considered “muchusar amana”. See Shulchan Aruch C:M 204:7, Rama ibid, Shu”t Chasam Sofer C:M 102, Shu”T Shevet Halevi 4:206, Pischei Choshen, Kinyanim 1:4.