They'd be foolish to do so.
Most CPUs are not overclocked. This forum is an extremely unrepresentative sample, as we all know. With some exceptions, overclocking is normally done by enthusiasts who have a lot more knowledge of the hardware they use than is normal.
For the sake of argument, assume Intel carefully picked what were effectively highly underclocked Core 2 CPUs to give out as samples. So, for example, they picked out the small minority of Core 2 CPUs that passed standard Intel testing at the highest speeds, say around 3GHz, and marked them as being rated at 1.86GHz, 2.13GHz, etc. Voila! The samples all overclock madly.
Sounds like a good plan for Intel, right?
Wrong.
Nearly all potential customers aren't going to overclock their CPUs. Most of them wouldn't know how and probably don't know what overclocking is anyway.
So the deceit you refer to would only affect the reputation of Core 2 amongst a very small part of the potential market - enthusiasts who know at least a bit about their hardware.
If the retail chips generally don't overclock anywhere near as much, those enthusiasts are not going to be happy. They'll know enough to recognise the dodgy marketing, the deliberate misrepresentation of the overclocking potential, and they'll know it was deliberate.
So doing what you suggest would gain Intel nothing at all with most potential customers and would decrease the reputation of Intel in general and Core 2 in particular with the rest of their potential customers.
It's possible that Intel are short-sighted enough to do it, but I doubt it.