Magnus looks rather surprised, as he thinks... So, knowing we have no knowledge of this Blacktree fellow, or his allies, Embrath wishes us to wander the city blindly, and trust in Blacktree's allies to seek whomever out? I can only assume his colleagues will be watching for this anyway. That means that whether or not we accept his deal, we advance his aims. Not that I'm complaining, but fair payment for services is not his goal. That means he's likely trying to either get us on his teat, or establish that we owe him something. As nice as the money sounds, I don't like strings attached to me, before I know where they are leading.
Magnus speaks up again, hesitantly... "When I stepped foot on Asam's boat, I had every intention of coming to this city and going forth into the town and conducting business here, and I still intend to. If that business helps you advance your aims, I am pleased to help. But I cannot, in good conscience, accept payment from you for doing what I intended to do anyway. If you must find a place for five thousand gold, please, split it evenly and donate it to the temple of Eldath and shrines to the Red Knight, and consider any debt you owe me for my assistance paid."
EDIT: @DM:SpoilerI've amended my 1st statement to match. Now I'm looking up an old friend, and seeking information on lost dwarven crafting techniques, with no apparent link between the two.