Unless I'm buying a vehicle for parts, I will NEVER buy one without a title ever again, at least not without REQUIRING the owner to apply for a lost title and have the replacement IN HAND before I buy it. I'll even pay to have them apply for it, but I won't buy it without one! Way too many hassles.
I bought my PSD off CL with no pictures... granted, the description was way rosy compared to the reality, but the mechanicals were good, very little rust, and the body damage (wrinkled bed at the tail but no frame damage; causes the tailgate to fall off when opened) is manageable.
As for what problems they have, here's a few problem things I've learned about in the three months or so that I've owned mine:
* Vacuum pump
* Tilt steering loose (depends if PO used it as a grab handle to climb in, mine did
* Turn signal switch loose/broken
* Dual-mass flywheel springs worn/broken (if manual trans)
* Clutch pedal loose (bad pedal bushing; again, manual trans)
* Trans slipping (auto trans)
* Bad ball joints/camber adjusters (if D50 front axle)
* Loose/blown frame-end bushings/mounts (if D50 front axle)
That's really about all I can think of. Not a lot of huge problems on these rigs.