DSLRs are just not free of dust or oil potentially,, so far, out of the box, mine have been mostly fine, but I have noticed sometimes dust, so, I clean that out myself. Just part of owning a DSLR is learning how to clean the sensor, tons of online videos showing how it is done. Cleaning sensors is just part of the process of digital.
I will say,, that with the vibration mechanism, my cameras have way less prone to dust lately, plus, I have developed a more of a habit of the way I change my lens,
get the new lens out,, take off back cap,,
put lens under left arm
hold camera down/and always downwind
flick off the lens, smooth motion
shuffle new lens into hand (while keeping camera held down/and downwind)
flick new lens on,,
back lens cap on taken off lens
total elapse time, 8-10 seconds
camera exposed time to the air (2-4 seconds)
I cringe when I am teaching a photo class, watching people switching lens, pausing as they start debating the merit of one lens to another, holding the camera up to the air, and they wonder why they get dust.
I can now go almost a year without the mirror up/clean mode.