That is a pretty good video though other than the box I had some different indicators and accessories, the IMEI missmatch might be a tipoff.
The biggest indicator, which you can't check before you buy, was opening them up after they failed, the circuit board looked like an ashtray, it actually looked like they had removed/swapped surface mount components to rebuild the phones. The biggest problem was the EMMC was degraded to the point that neither would enter flash mode no matter what I did. I have flashed good N900s even successfully testing the flash mode on another N900 when I tried to flash these rebuilds, there is a long thread on my attempts to save these phones.
Like I said I have seen people get these rebuild-from-trash N900s and be happy, at least immediately, one of mine was fine for a month but the other had a full contact book and some non-working apps that couldn't even be reinstalled. It is a neat small business hack getting these dead phones to boot, but not when sold at newish prices. My suggestion is that you only buy from individual sellers with obviously somewhat used phones, this is the only way I have avoided fakes. Being used it also helps find phones with tougher USB ports which have withstood the test of time.
I actually wish that these rebuild shops were part of this community as I suspect they have mastered direct jtag flashing and many other advanced DIY fixes which we do not have documented.
What is kind of cool is that the N900 is such a great phone there is a market for fakes this long after it's release.