I've had the same issue at times too; you'll attempt to clean off a bit of "dust" and it ends up smearing or appearing like a scratch. Not a big deal, don't freak out!
Just be patient with it; I use a lens cleaning cloth and a very fine tipped brush, and just gently wipe the dust away and keep taking test photos until all the dust is gone. I haven't invested in any expensive type of sensor cleaner, it just doesn't seem necessary as long as you are patient and have some common sense about it (AKA, be gentle
).
Cornflakes, good luck with your scratch. Hope you can wipe that thing out!




