I have looked up several posts to the Tingalf quest, but I have not been able to find out some answers.  People only put in what happened wrong with them, and I'm not interested in that!  The annoying part is, I can solve everything with the Tingalf quest, except get rid of the quest from Trevor in the Merchant's Guild.  I talked to him first, before Marcus and Lt. Robins about Tingalf, but now it seems that I can't get a prompt to end the quest for him.  My saved game takes place after I helped Maria, after I got the quests from Trevor and Marcus.  What do I do?  How am I supposed to get something from Trevor?  None of his speech options solve the quest.  I tried rearranging the order in which I solve quests between Marcus, Lt. Robin, and Trevor, but to no avail.  Can someone help me out?