If you search the forum you will find that some of us that have bought used S&W guns have be told by S&W that they are NOT covered when repairs were needed.
If S&W knows the gun was not originaly yours they will not cover it.

Mine was a police trade in (orininaly registered to the police department) that is now nothing more then an expensive paper weight. I have read on this forum about others also others having cracked frames and S&W said NO to warranty repair.

If you are fine with "hoping" you can decieve their CS then go for it.