I did look for an old & used double bass years ago looking round similar places.
One thing I found was that a lot of the basses I tried didn't sound good for pizz at all in the shops - my budget and amateur playing technique aside, they typically had really old strings and were maybe set up to sound good played arco, I don't know I wasn't an expert so just my guess. But tone wise they were pretty underwhelming.
Just something to bear in mind.
I'd recommend getting an adjustable bridge if you can, makes changing string type so much easier.
Best of luck,