Hello and welcome to the forum.

Even though the published Minimum Advertised Price for Karastan Original collection (700 Series) is $2399 for 8'8" x 12', I think you will be doing very good to get $800 or $900. (The market for used rugs is probably a lot like the market for used houses.) I would suggest local classifieds and/or Craigslist.

But note that getting even $700 - $800 is probably like having the rug for free for all those years because it probably cost something like that back in 1955. No, it generally shouldn't appreciate in value but there aren't all that many that hold their value either.

I have sold Karastan rugs for many years. They are machine made in the USA and typically beautiful and sturdy rugs, just not investments.