If you think that your tabletop or door is very old or valuable, you can take it to an appraiser who specializes in Asian furniture. If you think you know the value of your item, visit a local dealer who specializes in Asian antiques. Take several photographs of the piece to see if they are interested in it. If they are and seem to want to strike a deal that sounds fair to you, go for it. Of course, they will want to see the piece in person before they make a decision.
Selling a big, heavy hunk of wood on eBay or Etsy sounds difficult. Shipping would be very expensive.