it seems difficult for you to buy a good second hand pool table in Hanoi because people who want to buy that funiture usually put their ads on some website such as: raovat.net, raovat.com or others like that. But they usually let their phone number on those website, too. If you were a Vietnamese, it's easy to call for them and make deal with them to buy but you are a foreign person, how can you call and how can you find out those ads to call for or you can get their phone but you might call for a Vietnamese that he don't know English.
That's why I say "difficult"
You can buy easily unless you are familiar with a Vietnamese.
Hung.