Upload & Sell: Off
Don't use compressed air or gas of any kind on a DSLR sensor... all it takes it a wet swab kit if your blower (I have 3 Giotto bulb style blowers) doesn't dislodge any stubborn particles, and I usually get around to a wet swab clean on my camera sensors around once every year it seems, sometimes more (shooting motocross or horse events or baseball regularly tends to bump up the totals). Really nothing to be afraid of, and I do think it's harder than some people are led to believe to cause any kind of damage to the filter. Sometimes it takes 3-4 swabs before the sensor is perfectly clean when you get really stubborn spots, but I've never had anything I couldn't get clean. I think the stores and service centers will try to convince you that sensor cleaning is something you should leave to them and not attempt yourself because, well hey, they make money off it. But if you have some patience and a steady enough hand there really isn't anything you can't do yourself.
To the OP, I don't think it's fair to say "this is very common with Nikon", as I've had at least a dozen or more new Nikon bodies and never noticed any sensor dirt on any of them.
I have to say I tried an Arctic Butterfly tool and found that after three or four tries it actually made things worse than the original dirt I was dealing with. Wet swabs are simple, easy to use and effective.
I wouldn't return a camera body over a spec or two. But that's just me, YMMV.