The estimate stated Supply, Install, sand and finish treads and risers which means to me unfinished.
Our installer is trying to get away with installing pre-finished stair treads and risers which would be less cost to him in labor and material. The pre-finished were installed with 1/8 inch gaps along the stringer. I told him they needed to be replaced with what was estimated solid unfinished and installed correctly and he is arguing with me that they are just as good but I see it as he is just trying to cut cost. I also do not like the variations in the 3 planks it takes to cover each step. Am I correct by assuming pre-finished are less in cost for material and labor?

Let me understand correctly. Were the treads he installed all one piece OR individual floor boards (3) plus a stair nosing? How wide are the steps? 3' ? 3 & 1/2' ? As for the fitting to the stringers, it isn't easy. I use a stair wizard jig to measure and transfer the measurement. I sometimes get very slight 1/32" gaps here or there and end up puttying or caulking those. I think if he has 1/8" (if they are 1/8") gaps on both sides on every tread, that is a little sloppy.

The treads are 34 wide 10 7/8 deep measuring from the riser out. The treads are pre-finished 3 pieces Tung and groove including the 41/2 inch bullnose.

Actually the cost of prefinished flooring alone, is way more then unfinished boards. Depending on the manufacturer, it can be $10 a sq.ft. more.

Did you expect to get solid treads, or stairnosings and flooring?

Look at it this way... He sand & finished them before he installed them!

Gary,
Do you use this to save time or to increase accuracy (smaller gaps)? I have 19 stairs to install in our DIY job. We had a local installer consult us at the beginning of the job and he recommended using a jig like you mentioned. He said it would run about $100 - not a big cost for a pro, but not a cost I can readily dismiss for this one-time install.

I still don't get why they are short. That has nothing to do with the finish.

Both, actually. But a jig of this type is only good for for stairs with stringers on both sides. If your stair case is open on one or both ends, then you would be using treads with returns and the stair wizard jig would not be helpful.

My beef with stair jigs is that they are totally useless if the skirts have any crown at all. I find it quicker to make felt patterns and scribe the sides with dividers. I get it all right, back cut both sides plus a wee proud and then massage them in with a jitterbug if necessary. I will not caulk the side of a tread I charged 100 dollars to install.Caulk is temporary. My work is not.