Glad you found us, Mountainman!  
I think it is a great idea to check out the desk in person.  If you get any sort of negative feel to it, you can always walk away.  If you don't, it sounds like a great peice!  If the desk was built by this woman's great-grandfather, the spirit may be attached to her rather than the desk.  When and if you get it home, you may find that there is no knocking at all.  
I don't think having the item advertised as haunted scared people away on the ebay auction.  In the past, that has been a big selling point.  What may have happened, is so many people getting burned, thinking they were buying a "haunted" doll/bedroom set/shoes (yes, I saw a haunted pair of shoes advertised), and finding out that it was just a scam to get people to buy something.  I've heard of several unethical sellers using that ploy.   
![[Sigh]](graemlins/ohwell.gif) 
 
We've got several threads on the shows you've mentioned, be sure to check them out.  I get a kick out of watching them.  There is also one on  TLC called Dead Tennants which is probably my favorite right now.