Question about Saarinen round tulip table  

No problem
I've had most sizes of tulip tables and have never had a problem with stability. The vintage table bases are particularly heavy, the recent production less so but still support the table fine. Sine the round base is essentially one large circular contact point, if the floor is uneven it can make the table wobble.

I'd be inclined to accept the salesman's excuse.
An imperceptible unevenness of floor can make any table wobbly-- it's the only reason a metal pedestal of this type would wobble, isn't it? Think about it-- if a table has no moving parts, and it's teetering, it's teetering because of the floor.
I've never owned an extremely large Saarinen table, the only thing I could think of that would make such a table unstable would be a great amount of weight set on its edge. But that'd result in a crash, not a wobble.

Are you sure it was a...
Are you sure it was a Saarinen table? The Burke tables tip easily but the Saarinen ones do not.

No problem from mine. I...
No problem from mine. I agree it's either the floor or the table is a knock off. Saarinen was stellar and freakishly close to perfect in terms of design.

Knoll tulips
The design is not inherently unstable.Of course the surface must be reasonably flat,yet thick pile carpets esp in wool can shift the small ones...

if you pay a couple thousand...
if you pay a couple thousand for a table, bring it home and you think it's wobbly, i'm sure it would be pretty easy to return...