What to check when buying
 

Have been offered an XTX with 30,000 miles. What should I be looking for?what goes wrong? What price should I pay?

It's a difficult one that, at 30'000 miles it's a well lived engine, you need to make sure that the engine has been well looked after, I would have it examined by a qualified mechanic that you trust.

Provided everything is in good shape, I would think that a fair price should not exceed �2000 for a 30'000 miles bike.

good luck

Brake disks, these get expensive.
Chain & Sprockets.
Steering head bearings.

What price was it offered at? Max value if as mint as a 30k miler can be is no more than 2K although I have seen much lower mileage XT's on here for just over that.

Make sure its got a good service history, its a big single and likes to have its engine services (espically oil changes). Apart from this and the other things people have said you should be fine.