Movie's Last Twist

Does anyone besides me think that the ending is another twist? The bookstore window filled with books titled "Duplex" makes one think the book is a best seller. As it is accompanied by a banner with the title on it.... Big seller! YOu see that scene immediately after the old lady's question about what will happen to that nice young couple.
And, will the whole thing come back to bite the 3 who hatched the duplex scheme?
I can conceive of several scenarios and I found it funny to think of them, even though I also sometimes like endings that tie things up into nice neat packages.
So, they finally have money again, they're not broke. The agent wants him to do more books, his friend is jealous, etc.