You can't detect whether a systematic bias in the sampling method exists by looking at the results.
If you have a prior, you can.
In a slightly more unrolled manner, if the results you are getting are inconsistent with your ideas of how the world works, one hypothesis that you should update is that your ideas about the world are wrong. But another hypothesis that you should also update is that your sampling method is wrong, e.g. by having a systematic bias.
You know the drill - If it's worth saying, but not worth its own post (even in Discussion), then it goes here.