To answer your Question. There is NO guarentee.
I purchased a S&W Mod 360j that upon carefull inspection at the LGS looked and funtioned properly (owned & sold many guns over 50 years).After opening and closing the cyclinder 20 or more times at home,I noticed the cylinder was dragging and the front of the cylinder was losing it's blueing . Got the gun on Friday and sent it off to S&W 5 days later. S&W replaced the BOLT and touched up the cylinder face(I had opened the cylinder maybe 10 times over 2 visits before purchase and noticed no abnormal dragging issues).
On another New gun everything LOOKED ok but when shot the groups were 2" to the left. Factory replaced the BBL(bbl to frame fit was off).
If there is a S&W gun you want and the price is right,get it.
You can't always find or notice an issue with a new gun and S&W will fix any problem. JMO
Be SAFE and Shoot often!