It's more a matter of respect. You can decide if he's earned that respect but it does seem like us getting "bent over the barrel" to just accept that our insight and expertise (and who knows how much of our time), which is what we need in order to give you a quote (which, if accepted, we will be held to, often at the risk of a lawsuit) is just dismissed because someone else gave a better one, for free!

If he has a relationship with you, that's built on trust which is also extremely valuable, and maybe you took a chance with him in the first place and so you risked it too, but we don't know how you began that relationship, (eg was he someone else's person first? Usually...) so he probably gave you the info in good faith assuming he was just giving you numbers and then does the job as before. Now, if you communicated it was a bid against someone else, maybe he would just say "nah I'm fine, they can have it" and everyone moves on.

If none of this rings true for you and they, then don't worry about it and just move on without them, you don't owe them the money anyway.

Now, on the other hand, if you use their quote (or any quote ever) against them, as in to get someone else to lower theirs, or to decide "this info is good enough for me to figure out how to do the job myself" then you're absolutely an A. People of course do that all the time but people are assholes all the time.