Buy a watch you can research. An American factory movement with a legible serial, a grade name and a jewel count can be dated and described using published records, which makes it a teaching object as well as a watch.
Prefer completeness to glamour. An original dial, correct hands, matching case configuration and an unbutchered movement teach you what correct looks like; a rare watch with replaced parts teaches you very little.
Assume a service is needed and budget for it separately. A watch that has not been serviced in decades should not be run until it has been, and the service may cost more than the watch.
Read the description as a claim, not a fact. 'Original dial' and 'all original' are opinions unless supported by photographs, hallmark evidence or documented history; ask what the seller is basing the statement on.
Be sceptical of value talk. Any price figure is only meaningful with its source, date, condition and sale channel attached; buy because the object interests you, not because of an expected return.