I have written on this many times and it nice to see an article from DPI supporting how important it is that you learn how to do this yourself.

The main reason for that is if you are traveling you more than likely will not find a camera store where the service is offered at about 65.00 average.  It is a lot less costly for you to learn how to do this.

That said, there is an editors note in this article that says the dealer or person is directly responsible if the sensor or camera is damaged.  I would double check the store offering the service what their actual policy is.

I have personally cleaned sensors over 1000 times, maybe more and have never had a problem.  I use Sensor swabs and liquids.

How to Clean Your Camera Sensor in 3 Easy Steps.