Repair to set Trigger? If a set trigger would malfunction on a Custom SS German rifle pre. WWII, where would on go to repair it.  Considering my first SS   buy, New to site.
Regards mickey

If the basic action and barrel, stock are good I'd not let a trigger problem stop me if the prices was 'reasonable".  Missing/damaged sights might present more of a problem if you are seriously going to shoot them with 'iron sights". 
I've picked up several GI souvenir single-shot rifles over the years.  Almost all have had some sometimes damage messed up DSTs,  firing pins "safed" by having tips snapped off,  even oddball springs that are broken or missing.   Each and every one has been masterfully repaired by Steve Durren of Johnson's Sporting Goods in Adrian MI   (I'm really lucky to live within a few hours drive of the shop where he is the resident gun crafter--and he also shoots pretty regularly at the ASSRA matches at Etna Green).
There are other good 'smiths associated with our sport who are capable of sorting out and repairing germanic style DST systems.  Others will chime in with their personal recommendations as well.  Fortunately many of these euro-rifles have a removable lower tang that can be shipped easily for cleaning and repair.

I just had Steve Durren rework a little German engraved DST break-open single shot stalking rifle with a bad bore to 25-20 ss  It had claw mounts  I found a german claw mount scope with claws spaced almost right in evilbay for about 125.  Steve had to do some tinkering on the scopes mounts to get a solid fit and it has the old 50's style german movable crosshairs in a coarse 3 post reticle.
  The action was too small for any of the cartridges you are looking at other than maybe a 25-20 W    Possible it could have been redone for 32-20 with standard loads. 
    If the rifle you are looking at is one of the smaller Martini-actioned "stalking" rifles it might be a good prospect; though it might be a bit heavy for a 13 year old.
Generally the "stalkers" are a little less ornately stocked for hunting rifles rather than the elaborately carved and prong-buttplated target rifles and may have less complex "field sights' mounted on the rib-rail. 
  An examination of the action for condition and strength would be needed to assure safety, but one of these martini-actioned "stalkers" could be loaded to lever-action 30-30 or 32 Win special levels; or perhaps relined to 257 Roberts--25-35 win. or maybe even relined and rechambered for the 260-rem (though thats a rimless cartridge)  There is also the possibility  of a 6.5x35 wildcat by opening up a 25-35 to .264/6.5.

also PM sent