There's the note system thing on aw where you can make a private note on someone that only you can see. I use it to pop on notes like "enjoys rimming" or "likes face sitting" or "only likes half hour bookings" as well as little notes about when they like to book. If I have a phone number I save it on my phone with a description like "tall blonde" or "happy bloke" so I know who is phoning or texting. The odd one or two who have said they want to book but never do or send endless texts asking questions with no intention of seeing me I add as time waster etc or add to my call reject list.
One guy who I saw when I first started really took the piss, booking half hour and then only turning up with thirty quid, then wanted just a ten minute booking, really smelt terrible and refused to take a shower. I added his number to my phone as "smelly" and his aw name went on my block list, along with the guy who wanted me to travel half an hour to him, which would've cost me forty quid in taxis, for ten minutes for twenty quid.
No matter what girls say, we all keep some sort of reference on clients somewhere, even just saving their phone number with some sort of epithet. Detailed notes, however, for me, are a no no. In the wrong hands it would be devestating to punters, and is just compromising any chance of being discrete.