I've bought expired film off forums and eBay. So far, almost all of it has been fine. But I bought some 35mm Elitechrome 400, supposedly frozen since new, off eBay though and two rolls have consistently been bad. Muted, pastel looking colors and more grain than one would expect. It might actually be good for some subjects but I refuse to use it any more for general shooting (besides, Provia 400 is so good. Now if someone would make a 400 speed slide film with color and contrast like the lamented Astia or E100G...and type R paper...ah, to dream...)
I don't know whether to toss it, offer to give it away for shipping, or try cross processing it. I've never done cross processing and seen some interesting results. That might be fun.