NIkon D80 (Sensor Cleaning) Service?

I had got some Dust in my Sensor and since its the first time i gave it to K&S Photo for Sensor Cleaning. I got a call saying that "We have tried our best but still there are some more spots which we would recommend to send it to Nikon Service Center" My confusion is what went wrong? I'm going there tomorrow anyways, but Sensor cleaning is a straight forward process and why is it not possible to clean the Sensor by a reputed Service Shop? Something seriously Wrong with my Camera? I'm concerned. I Handle my Camera Gently so… Please let me know your inputs and what do you think abt Nikon Service? How much would i be paying for that Approximately?

Note: Please don't suggest that i can do my own cleaning and stuff, I'm fine to go with a authorised Service center cleaning.

I would never suggest you do your own - can get into even more trouble that way.

Nikon is a stand up, reputable company and I'd have to believe there service would be fine. Sounds to me like the first company you went to either doesn't know what they're doing or it's a scam. I don't want to be cynical about it but there's so many scams going on these days seems to be one on every street corner.

Cleaning a mirror is one thing, I prefer to be able to blame someone else if the sensor gets messed up or scratched.

More than likely K&S is being extra cautious. If it was me I would have THEM send it to Nikon. If anything is wrong with the sensor, and you sent it to Nikon, K&S can say it it was fine when they had it.

Since K&S could not perform the cleaning to your satisfaction, I would not expect to pay the full amount of their cleaning bill.