So, I have been trying to make fondant from scratch because no baker in town will even attempt it. I have tried three or four recipes that all come out WAY too sticky. Smooth and pliable, but fairly sticky. Having never worked with fondant before, how stiff should it be when I work with it? Anyone have a decent recipe or ideas on how to make it stiffer? They last recipe I used took about 9 cups of powdered sugar and was still tacky.

it might be beneficial to buy some commercial fondant (e.g. Satin Ice) so you can get a feel for what fondant is like.

also, climate can change how well fondant behaves. warm and humid make unhappy fondant.

I think that means you have to knead it more.

What recipe are you using? The basic one is 2 lbs confectioner's sugar, 1 pkg gelatin, 1/4 cup water to soften the gelatin., 1/2 cup corn syrup, 1 tsp glycerine and maybe 1 tsp shortening if you want to add that. I make my own fondant and use that recipe all the time, then if I need to stiffen it up I knead in some corn starch, or to soften it I knead in some shortenting.

Commercial fondant generally doesn't have gelatin, it just has gums in it, so it has a different stretch to it. I like the gelatin version, personally.

The most successful one so far I've been using 1 Tbsp gelatin in 1/4 C water, 1/2 C corn syrup, 1 Tbsp glycerin, 2-lbs powdered sugar and 1/2 tsp shortening for kneading. It seems fine at first and then get super sticky after it sets. Very not yummy. I'm a chemist by training so I am thinking that the glycerin may be too much.

Why not use the marshmallow fondant recipe. Always has worked great for me and tastes good.
Melt 16oz marshamallows with 1tsp water and 1tsp flavor. add 1-2lb sifted powdered sugar until fondant is to your liking. Simple. Roll with cornstarch/powdered sugar.