Should your word be your bond?

[Steven J.]

I just signed with a contractor using my own version of a @David Robertson and @J. Scott documents found in the fileplace. Upon signing, the contractor wanted to back out of installing quarter round at the wall/ceiling. He's mainly a drywaller installing new drywall and knock down on the ceiling in a hallway and bathroom. Is this a big red flag, pretty common, or not a big deal? Honestly, its probably a way to save me money as my TB can make this type of fix in the home themselves rather than myself. 

If I end up liking his work and using this contractor again I will call him on his word. Personally, I'm traditional because my word is my bond and if I break it it reflects poorly on me. I'd same something along the lines of 'don't say you'll do something if you can't deliver.' Thoughts?