I agree with Edwin Ashworth that the primary problem with the quoted sentence is not that it has omitted anything of value but that it is excessively and clumsily wordy. If, instead of saying
So they had every reason to keep a good relationship and, both for that deal and in general, to just sort of keep a reputation for being honest and for dealing fairly with people.
the sentence said
So they had every reason to preserve a good relationship and to maintain a reputation for honesty and fair dealing.
would you have any concern that something crucial might be missing from it?
All I've done in the revised sentence is replace "keep" (twice) with slightly more vivid verbs, shorten "for being honest and for dealing fairly with people" to "for honesty and fair dealing," and delete some dead—and indeed rotting—wood ("both for that deal and in general" and "just sort of").
Interestingly, although the original sentence's main problem was prolixity, the effect of its excessive padding was to lead you to think that it wasn't long enough (that is, that it had left out something important). I suspect that this effect occurs far more often than many people would imagine.