I totally agree with Garczar, those typical furniture grade tables are not serious playing tables, but... if you just want something for the family to bang around during Christmas vacation then they will certain fill that need.
What to look for? Well if it were me I would definitely pay a visit and check out the underneath to verify that it's a slate table and that it doesn't have any obvious issues, like cracks. While under there look to make sure that none of the hardware is missing. The rail cushions are secure. I would roll a ball around and into each cushion to check for dead rubber, loose rails. Are the drop pockets secure, those leather drop pockets are notorious for splitting the rail end due to kids wanting to do pull ups on them. You can count on having to replace the cloth, but everything else should be operational at least. If you need to replace pockets and/or rail rubber, or if the pocket angles are mushroomed then obviously take big dollars off the offer, or just pass totally on it. Personally if the pocket angles are mushroomed then I would steer clear of the deal all together.