The throat hit is a dead giveaway. I'm nic-free now, and I don't miss the nic very much, but I do notice the lack of throat hit.
Possibly, but not necessarily -- if you give it to them in a dripper or kayfun, you could easily fool them into thinking they're getting "nicotine throat hit" when it's just the device that's responsible. Conversely, if you give the ones getting nicotine their vape in a T3S or Protank, the TH would be so light that they'd assume it was nic-free.
The Virginia that I vape from MyFreedomSmokes has excellent TH in *any* nic level of their 85% PG blend -- I've used their 6mg and 12mg, and routinely mix those for my daytime 9mg, and I notice no diff in TH in any of those strengths -- another good way to fool test subjects into thinking they're getting a nicotine throat hit, use lots of PG. The only difference I noticed between the PG and the VG Virginia from MFS was the throat hit.
For what it's worth, if I go into a vape shop and try their sample flavors, which tend to have either 12 or 18 nic, I get a head rush from it.
Me too! But then, when I vape 6mg from a dripper I get the same effect, as well as a TH that sends me to my inhaler!