Just sold my old Amtrak locomotive. It was a 2001 AKN (150PS) with 173k miles for slightly more than your 2002 B6 (180PS) price. I love these cars, but after 10 years of ownership it was time to move on. Admittedly my one was in great shape with all the paperwork.
These are relatively old cars now, but if well maintained will run forever. I know the 180PS V6 suffered from wear on camshaft, and some examples had DMF issues, often because the B6 V6 could be chipped. Unnecessary in my opinion.
You want receipts and plenty of them. 10k oil changes are an absolute must. In addition, evidence the timing belt and water pump has been done recently done. Should be done every 5 years or 80k miles. Use a genuine Audi thermostat. Cost will be in region of £600+.
Suspension will probably be tired, so check for usual tell-tale knocks going over cobbles. Ideally replace the lot with Meyle HD upper and lower arm kit. Front and rear ARB bushes are inexpensive but worth it. Original dampers are okay but check for leaks.
Check the lights on the dash don't light up like a Christmas tree. ABS errors are time consuming and expensive, and is either a speed sensor or goosed reluctor ring on rear. Rear handbrake inevitable siezes. Search for a thread on B5 forum for my rebuild thread.
Get under the car and check the rear diff. If it's wet, walk away. Will need new drive-shaft or prop-shaft seals. At 100k miles I changed the diff oil for peace of mind. Came out like Mellow Birds.
Faults, battery goes on alarm, pixelated DIS, siezed wiper motors, rusty wings, blocked drains in bulkhead under battery. Also check CV boots at front for splits and broken coil springs.
