Quest not completing

[Apkarut]

The quest A rouges deal is not being completed. I have fulfilled all of the objectives and when I go to the npc calvin montague he shows me the text that you get when you complete your quest but when I click complete quest the text just comes back again.
It let me clicks complete quest but it doesn't actually compete it, it just bring back the text.

[AverageJoe]

Log out, close WoW, try deleting the WDB folder in your WoW Classic folder, then relog in and see if it lets you complete it.

[Holysymbol]

If the above does not work, make sure you are not using any AddOns that will automatically complete quests for you. I had a similar issue and disabling the AddOn worked.