ok, so i'm heavily biased... BUT! -people talk about rusted thru FATs, the last year of production was 1999, so the newest fats are 9yrs old. I see plenty of FATs from the early 90s & late 80s which are obviously much older. I'm kinda expecting to see rust issues on any steel frame that old! (thats been properly used!)
personally i'd consider any bike having rust issue problems after only a few short years, not 9 or more yrs! examples that spring to mind would be the nickel plated marin that had bad rust within 6months! thats a rust problem! my mate mark had 2 warranty frames in 2years due to rust!
the ritchey P21 i sold to chris had pretty massive rust issues & that sucka had been barely used!
I kinda feel sorry for FAT, good intentions sealing the tubes to prevent rust, ironically had more potential to cause rust issues... tho the same could be said for any sealed steel tubeset & that includes yeti (joes old sherpa springs to mind)
IMHO the classic FAT bottom of seattube rust issue is dubious to where the responsibility lies? with the owner for not taking the seatpost out & emptying water out of the frame, or FAT for not having a breather hole in the bottom of the seattube?
typically the bad news is usually more overstated than the good. theres usually a LOT of fats for sale at any 1 time (I know, I'm always looking) & only a tiny fraction have rust issues.
FAT being famous for rust issues is BS IMHO. if the head tubes cracked (manitou) back of seatubes split (klein), alignment was pi$$ poor (amp) or they rusted thru in 6months (marin team issue) then fair enuff thats reason for a bad rep.
if you've got any real knowledge of fat then the moans should be about mixed quality welding in the early days (later serotta builts are always better) mixed paint quality in the early days (flaking off), mixed quality head & seattube reaming on the earlier ti fats & v.rare, but occasional early broken ti-fats with cracked welds.
so FAT being a retro bike to avoid? yeh I'd check for paint bubbles & other rust signs as I would with any 10 or more year old steel frame, but they're deffo not 1 to avoid!
there is a side note to all this ranting
a few years back people built up retro bikes as they were cheap or (in my case) they wanted bikes they couldnt get hold of 15yrs ago.
with the current retro market being so buoyant, if you actually intend on riding the bike.you'd be getting better value for money buying relatively modern. (no, really! 12yr old rigid yo eddy for £400 or a 4yr old orange sub5?..)
...anyway were where we? yeh FATs are sh,te, dont buy em, even the NOS 1s, leave them all for me