Sorry to hear about your disaster. I too learned the hard way with a fairly new Nikon D100 (many years ago!). The repair cost was prohibitive so I sidestepped and bought a D200 as a replacement, never going near the sensor ever again! I've switched to Olympus now (more suited to a 76 year old) and have never had a dirty sensor since (they claim the sensor is cleaned each time the camera is turned on, and I have no reason to doubt them). As in many things, experience is everything!Because i could not get the sensor clean from my Nikon d7200 i decided to use tweezers and a pec pad with some sensor cleaning fluid and try to get the stubborn dust spots of the sensor with some pressure that i could not apply when using sensor swabs.
Well to make along story very short. I scratched the sensor and it now has a big scratch on it that is visible on photos and does not matter what aperture you use, visible from f3.5 all the way to f/36
My own fault, i should have been more careful and maybe use a cotton swab with the pac pad instead of the metal tweezers. I am afraid that it will be a expensive repair and not sure if i am going to have it repaired if it too expensive.
I contacted the shop and their practice is that every camera has a visual check to see if anything is wrong with the body followed by cleaning the sensor. The D7100 came from one of their shops and was first send to the central warehouse before it was send to me. Apparently the shop did not do the sensor cleaning before it was send to me, in the warehouse they do not do that. They had time because i ordered the camera on sept 30 and got it yesterday oct 5 and The Netherlands is not so big that it takes 5 days to get from one end of the country to the other end.You would think they would clean the sensor before sending it out to a customer. A used camera should be fully serviced before they sell it..