This is such an important counter because a lot of people use it as the only way to tell if a camera is new or second hand. I have searched through google but it looks like no one can prove this can be reset. Is it possible?
In general? No. For some specific models? Yes.
for some Canon models supported by CHDK, you can sometimes gain write access to internal memory counters.
some other models have two batteries (and a capacitor) and pulling both batteries out, waiting long enough to drain the feed capacitor, will zero all counters.
sometimes re-flashing the firmware will do the trick.
For this reason, if you buy a camera, do not rely on the frame counter but request a receipt or, if possible, verify the camera serial number on the appropriate site (sometimes you can ask a service centre. High-end cameras often have a device history record so that you can know e.g. that your "almost new" camera has had half its circuitry replaced three years ago. The data isn't online, but the service people can access it).
And if you sell a camera...
A: if you sell to some dummy, he won't check anything and you'll be able to sell him a used camera as new. But you would have been able to do so even without the hack, which was therefore useless.
B: if you sell to a non-dummy, he will check the frame counter, notice that it doesn't match the model age / dirt / scuff marks / gear smoothness / LCD luminosity / whatever, and correctly deduce that you're trying to pull a fast one. And you'll probably have lost the sale and your credibility; the hack in this case has been harmful.
The frame counter reset trick is likely to be worthwhile only on a very narrow range of buyer gullibility, and you'll have to balance the likelihood of pegging someone in that range against the likelihood of meeting someone in the wrong range, and the risk of misjudging where the mark actually stands.
I checked my camara's for it. I did changed two of the mirrorrooms, the counter is still showing a lot of counts 78000 and 90100. So hardware changes doesn't reset them.
In my opinion you should than hack the camera software to do that. I dont think there are a lot guys on the world who actualy wanted to do that AND succeded.
The best way to detect first or second hand software is to ask for a receipt? If he dont have one, its up to you to judge :)