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.