Do you think core sampling is a reliable method to make sure a concrete structure has reached the acceptable compressive strength?

The smitch hammer test can also lead u to a wrong way based on my experiences of using both methods since u may impact it on a wrong place or angle how ever i prefer to refer the ACI standard where it says in most criticsl and worst situations u better reffer to design safety factors before any distractive test.beside the point that witness samples can be very gelpful to know the real strength if concrete even if we do not appoint the difference between laboratory and field curing.

A core sample is ok because it is from the structure you want to test , but it is destructive.

Better to measure the strength of the concrete , in Dutch "Rijpheidsmeting". To make it simple, enclose two wires in the concrete and measure how the strength develops

well it the best worest one, yet,  there are other ways, but not as accurate as the core test- although the core test itself not that accurate though-

1.     Core cylinder strength are generally lower than standard cylinders due to construction site curing.

2.     Damage may occur due to the vibration of the core drill.

3.     Core strength is dependent on the location the sample was taken from,

I heard about the rebound hammers test, which measures the rebound of a hardened steel hammer impacted on the concrete by a spring.  but this tests the surface hardness of the concrete, which cannot be converted to compressive strength directly, because it depends on many other factors such the surface smoothness, finish, direction of the impact, coarse aggregate type and size and the moisture content, also the carbonation presence, but it has been used before to estimate concrete strength but the accuracy and the rebound numbers were have to be correlated. 

so far, i would stick with the core test