Hardly suprising then that if you walk in off the street, waving an easily-forged set of papers wishing to rent an easily-bent asset in the £50K-£250K range, that the people who to a large degree have their nads on the line are more than keen to ensure that the potential hirer isn't a muppet or a headcase.
You make an interesting point about the (non) secure nature of a PPL, as it is not even photo ID.
OK, now we have moved into the realms of fantasy. Show me a proven case of someone using forged papers.
We hear of idiots with no licence nicking aircraft while drunk and crashing. But going to the effort of FORGING a pilots licence?