Okay, so here me out.
This map of 1885 Hill Valley is from the Doctor Collector Back to the Future Time Travel Memories Tin [X]. It's probably my favorite BttF map ever because of how detailed it is.
In the upper right corner, we find the first of two legends that name the numbered establishments on the map. And number five, by far, made my imagination spiral: fortune teller.
The Fortune Teller is located just behind the bathhouse (number 4 on the map) in the Chinese camp (3), apparently just out of view when Marty enters Hill Valley at the beginning of Part 3.
Long story short: No Pines Marty totally sets up shop as a fortune teller just to screw with people/ make Doc mad because he's actually telling people about the future/ refuses to live in the blacksmith shop with him.
That's it. That's the whole thing.
Nope, it was there the first time Marty walks into Hill Valley.