mav asked of proffer an offer that is made out of politeness or some other such constraint?

Wow, how fascinating. While I grasp, and agree with, the sense of proffer you mention, the idea of politeness as a form of constraint has almost never occurred to me. On reflection, I can see that there are times when it has an element of artifice and compulsion about it, yet, for the most part, it seems to me no more of a constraint than respiration.