We spent over two weeks there exploring the city and many surrounding villages which you can read about in our blog which should be linked in our signature below. Here is their website. They show the correct coordinates. 17.03095 -96.59902
https://oaxacacampground.wordpress.com/
And here is a picture of the paint store at the corner of the road you turn in - painted pink - can't miss it. This is from Google Earth Street View which works right up to the entrance gate to the campground even though it is dirt road.