Determining the health of a part?

Folks - someone has offered to sell me a set of landing gears.

How can I determine they in good condition, that is, any repair that
may have occurred and is not visible was done in a manner that won't
fail on me? Is there an examination the A&P can conduct i.e.
magna-fluxing (yeah, I know that's a term used in examing a crank, but
I don't know another term to use)? Is testing so expensive that buying
a used landing gear isn't a good idea?

Not that anyone would willfully sell a defective part, but I can see
the case where someone might have straightened out a strut and kept it
around for whatever reason, and his widow sells the part to someone
and had no idea the part was unsafe.

Regards, Mike