It is known that selecting control is the most critical and difficult part while conducting a case control study design. For getting true association , it is imperative that controls should reflect the exposure pattern of the source population that give rise to cases. What are the ways of selecting controls to be closure to true association?
See attached extract from Rothman Greenland 2nd ed which answers your question
This question is very difficult to answer because it depends on what you mean with the "true association". But you are right in saying that the right selection of controls is key. This paper gives a good overview how and when causal effects can be identified in case-control studies with different control sampling schemes: Article Identification of causal effects in case-control studies
https://sphweb.bumc.bu.edu/otlt/mph-modules/ep/ep713_case-control/ep713_case-control5.html
The comparison group ("controls") should be representative of the source population that produced the cases. The "controls" must be sampled in a way that is independent of the exposure, meaning that their selection should not be more (or less) likely if they have the exposure of interest.
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