I suspect if buying a used or refurbished camera (an M5, for example), you will not be able to assess the number of shutter actuations by looking at the file number as it will have been reset (at least that is how my 5DIV showed up) or you will not know if it cycled past 10,000.
For Shutter Count, under Q4 of their FAQ, they actually cite an issue that prevents access to the data:
EOSmsg.com claims to support the M and M2. But I could not get that to work on my machine even after downloading.
EOScount, which previous to the 5DIV is what I've used, does not report supporting any M series.
Sean Setters told me that his Dev friend told him basically the same thing as the shuttercount people did, it's inaccessible and in his words 'crippled'. Ok I'll just shoot photos with it no matter how many times anyone else has done prior to me.