A list of countries whose figures I certainly don't trust includes, but isn't necessarily limited to, Iran, China, North Korea, Brazil, and Russia. In a couple of cases this is because it's manifest nonsense: North Korea is still reporting exactly zero cases and deaths, for example.
Everywhere else, it isn't so much that that I don't trust the source but that the figures are likely to be an undercount to some degree or other. We've seen large spikes in death rates in some parts of Ecuador, for example, which can only be attributed to Covid-19, but the official death toll (based, perhaps, on confirmed positive cases only) is something like 10% of the likely actual.