Three things before I buy any vehicle:
1 - Title in hand?
2 - Smog certificate in hand?(if required)
3 - Willing to go to local Auto Club office and immediately do the paperwork and registration. (any glitches will show up on their computers just like the DMV)
If the seller has an issue with any of this, I walk away. Unfortunately, that seems to be more than half of the vehicles that I look at. Sigh.