Any TDI owner who is not at the very least well-informed enough, and acquires a VAG-COM and some of the special tools, is in deep doo-doo. Even if you are on the good side of a very competent mechanic who will let you watch over his shoulder and check up progress, you still need to prime them on the fundamentals and ins-and-outs, because it would be totally prohibitive for them to do the learning themselves. Dealer repair shops are absolutely out of the question. Even if the cost were not prohibitive, there isn't a single one with TDI competence or who gives a single shit about your car.
Replacing the timing belt is a major, major operation involving dismounting the engine and supporting it, lining things up with special jigs and tools, and replacing every part in the path of the belt, including water pump, tensioner, and all rollers. Then you have to set the tension very precisely, not rotating the tensioner the wrong direction because it's opposite to that in a gas model, and finally nudging the heavy injection pump by thousandths of an inch to get the injection timing in spec, using the VAG-COM to check it. And if you're off the scale advanced or retarded when you begin the adjustment, it's a special adventure to find your way into the window so you can see anything at all on the VAG-COM. Or get it running at all.
If the timing belt ever strips teeth or skips more than a single tooth, you are in dire danger of doing several thousand dollars of damage to the engine, or totaling it.
Then there are the special cute things that can go wrong, like an injector that sticks open instead of pulsing properly. That will turn it into a blowtorch that will burn right through the top of the piston.