No, the timing belt usually looks well used until it snaps. Often, the outside of the belt looks fine, the inside slips a tooth and boom. Don't forget the tensioners, bearings, water pump, etc. Budget it into your purchase price if there's no records.
If you're looking at a 2005-2006, you might want to wait a few months if you can. The new TDI is coming out and the MSRP is $22-23. Most of the 2005-2006 are asking $24k, it's a total ripoff if you ask me, and after the new TDI comes out their prices will come down to a reasonable level.
Don't forget that sometimes when they have the timing belt freshly done it's not done right. Look for paint match marks on the sprockets. Otherwise, a timing belt with 80,000 miles doesn't look signifigantly worse than one with 30,000 miles because they are supposed to stay strong for the rated life of the belt. Also remember that a diesel 4 cylidner engine's rotation is more jerky than say, an inline 6 gas engine and that puts stress on a timing belt.
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