Dragunov features, starting with items clearly visible in joe6pak's picture:
- "Waffle" shaped reinforcements stamped in magazine
- Single-piece stock forearm that is removed by sliding towards the front
- Stock forearm partially surrounds rear sight
- No rear stock cheekpiece, or a separate adjustable part
- Many US-market imports were sold without a muzzle brake
- Distinctive pronounced "S" curve in safety lever (not visible in picture)
- Large trapezoidal ejection port (not visible)
- Tang not visible at buttstock-receiver interface (not visible)
PSL features:
- Distinctive "X" shaped reinforcement stamped in magazine
- Two-piece stock forearm with horizontal joint
- Stock forearm does not surround rear sight
- Integral cheekpiece
- Normally has a muzzle brake
- Straighter safety lever
- Smaller rectangular ejection port
- Visible tang and screw and bottstock-receiver interface (not visible)
AFAIK the scopes interchange, so they are not a 100% reliable spotting feature.
Dragunovs are a good deal more valuable than PSLs; $1,000 is a great deal for the former, but NOT for the latter, they usually trade in the $800 neighborhood. Be aware, however, that a LOT of people do not know the difference between the two rifles!