You'll have to forgive my skepticism, I work in law enforcement... it comes with the territory.
However, I'd like to understand why people buy gear, and list it in the buy/sell area the same day its received? Or list "NIB", or never opened gear? I've seen ad's for everything from camera bags, to flagship camera bodies.
If an item was received and a person decided they 'just changed their mind', wouldn't it be more better for that person to return the item to the supplier they purchased it from, instead of taking a loss?
If its old gear that's been discontinued and its been in the back of a closet, I can understand the sale. But if its items that are just released, and not even in stock in stores I find it a bit suspicious.
How do you verify the stuff you buy hasn't been bought off the back of a truck in an alley somewhere? Or am I the only one concerned with this issue?
Just ask if they have a receipt. If they don't and you're not comfortable with it, then don't buy it. People do it to get cashback on their credit cards, rebates, airline miles, bing cashback (when it was around), or because they bought a package and are selling off everything they don't need. One of the best deals was when you could get a $400 credit with a Canon printer + DSLR, plus a double rebate when you bought a DSLR + lens. I got a 70-200 2.8IS v2 for $1700 once I sold off all the other stuff. Everyone that bought from me got new gear with a full warranty at a good bit less than retail. The point is that they might have their reasons for it, but as long as they have a receipt, you should be all good.
Also, there is a very good feedback system here on FM. If somebody was gonna do some scamming here, it won't take long to find out who they are.
Yeah agree with ndirienzo above, most sellers of BNIB items here are probably people who got a good deal on it for whatever reason (sometimes if you know somebody or you yourself work for Canon for instance - you might be able to acquire new Canon gear for cheap). And then they just come here to make a little profit.
I'm a cop shrink your intuition has saved your life, your partner's or both of ya'll's, more than once. You see it offered here and your bullshit detector goes off, trust it. The one's that are toughest, just as on the streets, is where everything seems so normal and straightforward, until the moment it ain't
Agree with the rebate and points as was said. Another thing to think about are those who break up kit purchases. I made a purchase last night on a new lens that was part of a kit. The guy breaks them up and makes a few more dollars on the transaction. I got the new lens for 20% less than a retail boxed one.
Heck, my local grocery chain offers $.10 off a gallon of fuel (and sometimes $.20) for every $50 in gift cards purchased. If you had gift cards from someone and added to them to pick something up for resale, you could convert the gift cards to cash and get yourself a nice discount on a fill up. (my truck costs nearly $100 on a fill up)
Actually, if you think about it, this is no different than those people who do extreme couponing. they look like they stole a grocery store truck but in reality they used the policies and coupons of stores to their advantage then turn around and sell the stuff for a small profit.
I'm also seeing really bad photos of items, supposedly taken by advanced photographers. They look like Ebay point and shoot shots. Buy and Sell is not what it was a few months ago. B&S is being infiltrated by aliens!
your intuition has saved your life, your partner's or both of ya'll's, more than once. You see it offered here and your bullshit detector goes off, trust it. 
The one's that are toughest, just as on the streets, is where everything seems so normal and straightforward, until the moment it ain't