I want to buy a vintage steel-frame road bike.


Dirt Disciple
Depends on your budget. If you like the look and design of the Trek, they are good. For the price you are paying for a Trek are there other options like Daccordi, Moser etc, as a comparison.
As for condition, I suppose it's like looking for a secondhand car, condition is key.
Paintwork, dents, drivetrain, rust in tubes. Look for those issues.