Phil has summed it up rather well, above, and I'd just like to add that the process
of a shutter replacement in a Canon camera requires decent knowledge of electronic
assemblies and micro-mechanical mechanisims.
This is not to say that it can't be done by a non-Canon technician, but to stress
that the process requires something of a working knowledge of electronic
and small mechanical assemblies. If you understand how an electronic ribbon
cable attaches to another component, and understand how a bunch of seemingly
unassociated screws hold together the case of any given electronic device, and have
a basic understanding of how these electronic devices interconnect together while
knowing about the differences between the various interconnection methods,
then you're all set and ready for undertaking a repair on your own.
You may also need to know some soldering techniques, as Canon assemblies are heavy
on ground-wire connections, from my own experiences. I replaced an A690's broken display
recently, only to discover that the assembly is grounded six ways to Sunday, while the actual
assembly is grounded 'till the cows come home. Grounding was accomplished with the metal
frame of the camera, and has served well through a 10-day visit to the Arctic Circle.