Tracing vintage equipment serial number #39nnn

In the case of an ad posted on a well-established website, how should I trace a particular audio component - well-established brand - using its serial number? I am speaking of a Thorens TD-124 and at this point I shall only reveal a partial number - I am obviously and cautiously vetting legitimacy. Perhaps an owner has the serial number marked on a left-over document and wonders whatever happened to it. 

Feel free to opine!