Yep had these over the years, one guy said "I'm married can't phone showing my number got to be discrete", err and 60-75% of my clients are married and manage to show their numbers no problem.
One chap after his 3rd or 4th call requesting a short-notice booking was told "If you can't phone and display your number there's no point phoning again because even if I was available at short notice I'd not give you a booking without a number". His response "Oh ok" and I never heard from him again, or if I did he did show his number.
After learning that withhelds are unreliable, cause all sorts of problems in arranging appointments(phones to confirm or say he's early at same time as another unknown number, and you end up playing cat and mouse because you can't phone him back to say "Come on over", or even more likely another person uses the same name and you tell which one is confirming/cancelling/asking for the pink lingerie). Or want to phone every week for 2 years asking the same questions pretending they've never spoken to you before.
Obtaining a call blocker facility was the best thing I ever did.