EnjayIs it relevant exactly what details they gave?
yes Address? Phone number?
it gave both, but there is more Could Geoff tell that all of it was false?
yes Part of the details?
no Did he recognise the details?
yesTreborIs the car in a parkade? Parked on the street?
Assume this - and I learned a new word! In a open-air parking lot? An enclosed one? Is it relevant what part of his car was damaged?
no If so, driver's side? Passenger side? Front? Rear? The roof? The undercarriage?
n/a to allRIght-hand vs. left-hand side driving relevant?
no Could he tell whether the person who wrote the note was left- or right-handed based?
no (Based on smudged ink, perhaps?) Did he know that the details were false because they were his details?
yes! Because they were impossible details to have? (Such as the person gave their phone prefix as starting with 555 and no one has a number starting with that?)
noDoes it matter how the car had been damaged?
no What age the other person was?
no Were they, or were they pretending to be, a child?
noPeterDid the person leave their name and phone number?
they left *a* name and phone number Is there something unusual about either?
not per se, no Spelling relevant?
know Does he know the person the note purports to be from?
yesEarnestare all the details given false?
yes Just a part?
no Did Paul need to read all the details in order to spot that they were false?
no, good Q (on the contrary, maybe he could just have read the name and recognized that it was the name of someone living abroad or the name of someone famous/not existing; or maybe he read the phone number, turn and recognized that it was the phone number of the nearby she-...)
no to examples, but explore this.Also, his name is Geoff 
Did the fact that the details were false prevent him from recognizing the faulty person?
yes I mean...maybe it has been given a personal card on Geoffs' car windshield?
yes! Maybe the personal card of someone he knew
no/his same personal card?
yes!! (difficult to say but at least he could have spotted that the faulty person was his client/someone he knew/a colleague...)
he may have had cause to be suspicious, but there would be a lot of guesswork
Relevant where Geoff lives?
no Where the hit and run happened?
yes, for context Was his car parked?
yes Relevant?
this would have been less likely to happen if the accident occurred while driving Could he see the car from his office?
most likely notDid the one giving the details voluntarily gave false details?
yes Maybe he just made a mistake and Geoff could not contact him anyway?
noGalFiskDoes he know any of the true details?
no Did the forger make a mistake?
yes Can he tell because ha has certain special knowledge?
yes Because of his profession?
no Do the detail point at another person?
yes No person at all?
no Are they cobbled together from the actual details of several people?
no WAG: does he work at a phone company, and knows that the format of the phone numer written doesn't exist?
no***** SPOILER *****
The person who had caused the accident had a grudge against Geoff, and wrote 'sorry' on the back of one of Geoff's business cards in an attempt to discredit him while escaping detection. Unfortunately, he hadn't realised that the car he had hit in fact belonged to Geoff, so the ruse fell apart very quickly!Well, that went quickly. Much like the car, until it hit the other one. Ah, well. Good to be back in the saddle. Congratulations, Earnest and Trebor. I'll think of another one, soon.