1) Lots of epidemiological papers about the Wuhan epidemic use data from phone carriers (not the government) to track the spread and make predictions, and they were generally pretty good with their forecasts. The numbers reported by the government are consistent with the forecasts from scientists.
2) The numbers reported by China are also consistent with the spread observed _outside_ of China. You can't lie about the numbers because every other country would detect an anomalous number of imported cases. (Case point - In Canada, we're importing way more cases from the US than you'd expect if there were actually only 1200 cases in the US. This is rather because the US is lagging so far behind in testing, rather than outright deception.)
The absolute numbers don't even matter that much - what matters is the trend and the number of new cases going to zero. Look at epidemiology paper - they always assume only like 10% of infected cases are tested and confirmed. The epidemic really is coming to a close in China, still gaining momentum in Europe, and coming in a big way soon to North America.