Yes, any usage or non-usage doesn't matter. Important is: who is the seller? Buying from private person is considered second hand, also because of the legal implications (hint: Lemon Law). So it's pointless to argue about the mileage or shutter counts or 'box never opened'.
The moment an item has been bought by a consumer, it is by definition "second-hand" if they try to sell it off to another party.
The only exception is when the consumer bought it and never used it. Even then, there is a price penalty to pay (because if I can buy the item from an established shop where I have possible modes of redress if I'm unhappy, versus off the open B&S market where there is little or no regulation [and thus possibly no mode of redress], at least to my knowledge, I am still taking more risk). Fact of life.
I will see that as a second hand no matter how nice the words were phrased.
Once item has left shop , as long as even if I just opened box to test , it is a 2nd hand item. One camera shop owner in Peninsula told me this before : it may be even that seller drop the set within the 1st week of use and wana sell it for peace of mind but u will never know if ad says 'one week old'.
End of the day, check with due diligence. I was cheated once due to being too trusting. Never take words at their face value, test and check , check and test.
Irrelevant. A lot can happen during one test. Take it as 'has been used for at least a short period' and inspect it properly. Take things like remaining warranty period as a bonus, not as a must. (If it's a must for you, you better get a local set from the shop.)
Technically speaking, once it leaves the first buyer, it is considered second hand. So if first buyer passed to friend free of charge, it is already second hand. First buyer buyer didnt use or open, transfer to someone else, also second hand.
In BnS, one should be more concern about the usability and condition. So terms like used once, never opened should matter little.