Buying a used string instrument, what does one need to know?

I'm saving up for another ukulele, or maybe a guitar, or possibly a mandolin.   Haven't decided yet and I'm a long way aways from buying.

Someone offered to take me around the music shops next week so I can get a better idea of what is available in town.  Then I can save up for when I'm ready.  

It's exciting, but also scary.

I went to a pawn shop recently and the strings instruments were either badly broken or obviously never played.  And when I looked the ones I remembered later that day, the used ones were all about 30% more expencive than the new.  Even the mandolin with the concave top was $100 more than the same make and model new.  Even I know a mandolin is not supposed to cave in at he bridge.

I'm hopefully next weeks expierence will be more pleasant.   I think it would go better if I knew what to look for and dint look like a completely new to instruments.

What does one look for when buying a used acoustic string instrument?

Depends on the instrument. For example a cello has a much taller bridge than a violin, and under higher string tension, and so bridge warping is more of an issue to look out for on cellos than on violins. With mandolins and guitars you have frets to deal with—are they cut properly, are they worn, etc. Tuners on a classical guitar operate differently and may have different issues from tuners on a folk guitar.

So in the absence of more detailed information, I would say play the instrument, making sure your left hand is feeling up and down the neck, paying attention to how it sounds and feels. Consider things like whether it’s intonated properly, whether there are any “dead” notes, and whether it ever feels awkward or like your hand is getting scratched by something, etc.

Also keep in mind—this is more true for electric string instruments but still mostly true of acoustic instruments—everything is fixable.

Tuners on a classical guitar operate differently and may have different issues from tuners on a folk guitar.

Could you tell me more about this?  I know some guitars aren't meant for steel core strings, but I didn't know the tuners were different (except the ones with the cut out head).  Is it related to string type and the big rod in the neck?

I learned on my recent ukulele setup experiment that I perfer geared tuners to ones that stick out the back and have a one to one ratio of turn to tune.  Like shiny violin pegs but smaller so they are more fussy.

Looked at some used instruments lately.  Very interesting expierence.  No decisions made.

Some needed a lot of love.  Probably more than I could give it like fixing a dent in the side or putt the bridge back on, refretting, that sort of thing.

I tried some of the good ones in my current piggy bank size and came to the conclusion that I am now ruined and would be unhappy with the $150 yamaha.  The guitar I have been learning on is too good (parlor set up for classical).  

There are suddenly string instruments in the charity shops.  Better prices, but less confidence in my ability to tell a lemon from a les paul.  

Although there was a mandolin that was a good price.  It says Ibanez, but isn't made in japan.  The materials like the cellulose plastic tuners was stoped being made before ww2, and it says (in spanish) established 1881.  Not that i need to learn the mandolin any time soon.  But i don't think it would be so cheap if the thrift shop manager knew how old this was and it's not a modern Ibanez.  But there aren't many of the spanish made ones kicking about, so maybe $50 is all it's worth.  Might be worth snatching up

My fingers are still sore from the steel strings.  Nylon string guitar or instrument are much more my style.

About half of the instruments I find at thrift stores or garage sales have broken bridges, or lack saddle or nut. Sometimes the tuner needs replacement.

I sometimes do pretend luthier work, and use a combination of bolts, clamps, and epoxy to reattach a broken bridge. As a non-professional, my work seems good enough for my personal use. I can't tell that I damaged the sound quality.

Over the years, I have gotten better at looking for hard damage like that.

The "other half" can't go past a used instrument shop, so with that in mind here are some observations.
Is the neck straight - sometimes they develop a slight twist.
Are the frets all the same height and none of them off line
Do the tuner keys stay put under tension
Is the timber sound - no cracks
Nothing unglued
All parts there
Does it sound right - no buzzes or weird tones
Is the price right!!! given any faults that might be easily fixable.

As far as steel strings go, it is possible to develop the calluses and strength through practice. They are inherently harder to play, though. If you like the sound enough, and the instrument fits you well and is ergonomic to play, that can make up for the effort put into developing calluses and strength.

And regarding unglued parts: in mandolins and other instruments of similar design, the bridge isn’t supposed to be glued down. And if it isn’t present, it can be added or easily switched out.

M Ljin wrote:
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And regarding unglued parts: in mandolins and other instruments of similar design, the bridge isn’t supposed to be glued down. And if it isn’t present, it can be added or easily switched out.

Ah....

The guitar I was considering, had the bridge coming unglued.  More and more, i feel it isn't the right instrument for me.

The mandolin has the bridge glued down. But it feels like a really old kind of glue circa 1940s or 50s. Very brittle where the glue beed was seaping out from join.

Kind of the reverse of what we want.  I'm going to keep saving.  But I learned a lot looking at the instruments in person.  There is so much variation.

Further research suggests it's a Salvador Ibáñez mandolin, made in spain, circa 1920 (made by him or his sons).  Definitely not the Japanese made Ibanez we know and love today. It looks like it was played a lot. Other than the bridge, it's in amazing condition.  But I am not in the market for a mandolin and don't know how good I would feel playing on an antique instrument.  I would fear breaking it.  But there is cool factor and the curious question of why it's so cheap.  Maybe the charity shop manager mistook it for a more recent instrument?

If the bridge is in the right place, I don’t think it should hurt that it’s glued. Maybe someone got tired of adjusting it every time they restrung the mandolin.