I posted a link to an "02 ZTS Zetec about a week ago and finally got to drive it today. The body is in great shape and the interior is in good condition. The car has 83k on the odometer. It took it on the interstate and it hummed right along; I was actually a bit surprised at how well it drove. Overall, it appears that the car was well taken care of. The water pump and timing belt were replaced recently and the tires have about 40k left on the tread.

Question: What problems (assuming the transaction goes through) should I watch out for?

Replace the ignition cylinder with the new upgrade, Mike at the Hillbish Ford forum can help you out. It's an easy swap, especially compared to waiting until there's a problem with the old cylinder.
He can also run the Oasis report and tell you what's been done to the car. There was a fuel pump recall and you want to make sure that was taken care of too.
Good Luck!