This tutorial has made it’s way around the blog sites and was posted on /cgl/ about a week ago. It’s a promising guide that shares how to get rid of the shine on a wig, and it looks to have some great results! I was a little skeptical of this change and wanted to try it out before sharing it with you all so here are my results.
Someone on /cgl/ commented that if this works, we should just buy cheap Halloween wigs from now on to save money. Sounds great in theory, so I tried this out with a Halloween wig.
Before:
The wig has been colored with sharpie but has no other products in it. The base is a long blonde wig from Party City, the kind that is usually sold around Halloween. The wig definitely has a lot of shine to it, that is visible without the flash being used.
I followed the directions above, placing it in a large bowl. I added more than 1 cup of softener because the wig I used is longer than the one in the tutorial. I used enough Fleecy fabric softener to cover the wig. Then I left it for five days.
After:
I pulled it out, rinsed it off, and let it dry.
The colour faded from the wig, as expected. The shine was dulled a bit in the indoor lighting, but in person it is sill noticeably shiny and it is still highly visible with the flash.
The wig smells great, and it is a bit easier to run your fingers through it without tangling but overall there wasn’t that much of a change.
Could this still work? In the original tutorial, the author lists Talc as one of the products used. Talcum powder, or baby powder, probably did more to dull the shine in the wig than the fabric softener. It is also possible that the type of wig or fabric softener (both were unlisted) could have provided better results. 
Conclusion:
If you want to test it out, it’s a low cost method that may work for you. If nothing else, fabric softener is used to detangle a wig, so you may find your wig easier to work with afterwards but I don’t suggest relying on this method for all your future cosplays.