Can I Decline an Offer (Unofficial) that I have Accepted

[Penemonie]

I accepted an verbal offer from a faculty in a research university. I am expecting an official letter offer to sign. However, I just came to know that I might receive an offer from a program that I rank higher. Therefore, how bad will it look if I accept the new offer from the program and write a thoughtful letter to the faculty from the first school before officially signing his offer?

Edited March 25, 2017 by Penemonie

[limonchello]

You never signed anything - student OFTEN change their minds and they will be understanding.