Attention, layman’s opinion, no legal advice!
The engagement of A with B has nothing to do with the brokerage contract between B and C.
Ok, then let it come to that. The fiancée signed something with the broker, which, as far as I understand, was a declaration of intent - that is not exactly trivial. Now the deal is falling through because the fiancée (allegedly) does not (alone) have the corresponding funds or was not authorized to sign on behalf of the financier to purchase the property.
And then we get a law student from the first semester to dissect it. It takes 5 minutes and the broker won’t be able to sleep from laughing, because he will very likely receive compensation from the failed deal (lost turnover/profit) (of course only from the fiancée who signed the contract)
and can sell/offer the property again.
I mean ... if you can sell a thing twice ... who would be at a disadvantage? The broker?
Even at the risk of repeating myself: just the energy spent here trying to pin an error on the broker in order to get out of the matter strengthens my suspicion that the broker acted completely correctly and also provided information.
Best regards
Dirk Grafe