How do I buy a used trombone?

[u/AccomplishedMess6354]

I've been thinking of buying a student trombone after hearing there are usually plenty around.

As a beginner myself, I wouldn't know how to assess a used instrument.

Usually the advice is to go with someone who can check it out. However, I just wanted to ask here first - maybe it's easier than I think?

UPDATE

Thanks to all those who replied. I have found a Conn director online but photos only, no dings. Would this be pretty reliable? I'm a bit nervous bc I can't check it myself, it would be freighted. Cheers.