Hmmm, I can see no reason why this shouldn't be legit. OK the price is low but we don't know what's behind it. He may have been curious to find out and done it as an experiment and is now selling it since, like many others, he/she was just curious. He/she might even have wondered if there was a demand for them and have done it as a prototype.
The equipment needed isn't so difficult to come by or use, if you know what you are doing. I imagine a lot of people in Russia would. And, I know people in the UK with small workshops in their back gardens who found they couldn't sell them as people didn't make things from scratch any more.
As for click stops on a lens, it's usually just a hole drilled out and filled with a spring and ball bearing opposite a lot of "v" groves. So a drill and a hand file would be all that's required if the innards were suitable. Blacking it wouldn't be too difficult either.
Perhaps the problem is that too few people in "the west" have hands on experience of engineering, which is a shame or worse if the Chinese realise what could be done when they've the only real engineers in the world...
Regards, David