Well, if what's going on is what I think it is (and I hope it's not) then the deal will fall apart at the closing at the latest. The best thing the seller can do is seek legal advice from a real estate attorney. Heck, any time one is buying or selling real estate I always recommend having an attorney review everything before the closing. Then if possible have the attorney present at the closing too.
Now I've yet to actually sell any real estate in over 20 years now, and laws have changed a lot since then. But I've been through four closings myself as a buyer. One thing I've always done is to demand a copy of all closing documents at least 24 hours prior to the closing appointment so I can review them. On every single closing I've always found mistakes in those documents, that had the potential to cost me dearly down the road if I were to have missed them at the actual closing. When I find those mistakes, they're the first things I point out at the closing, and it's generally no problem to get them corrected right there on the spot, so that I'm signing a 100% perfectly correct document that has no "corrections" annotated on the document itself.
