Hi,

I just got my 629 back from Smith and Wesson Warranty repair to fix a dinged muzzle crown with burrs on the lands and a negative sear engagement.
The muzzle repair was flawless and the trigger is fixed and with a 3 pound pull with no creep. Very nicely done. Obviously done by someone that knew what they were doing! Bravo.
BUT
I used a feeler gauge to check the gap between the forcing cone and the cylinder and found that while the the .006 gauge slides in fairly easily the .007 gauge also will slide in but only on the left side. The Gap is wider on one side than the other.

Is this something I should worry about

Wouldn't worry me as long as endshake and yokeshake are ok.

How does one check? Is a 007 gap too much?

It's fine. If you search here for endshake you will find lots of discussion.

I think I would sell it and buy a better built specimen.

I have several S&Ws that exhibit the same. They all shoot VERY well. As in accurate.

Nearly all the guns I have came with a gap that was different on one side than the other. The minimum barrel/cylinder gap for lead is .006 anyway, so yours is as good as it gets without custom work. Keep it and shoot it.