If you ask "WHEN would you like to rebook" It not only sounds a bit 'pushy and agressive' but this also gives the client the option to say, "Oh, I don't have my diary on me, I'll give you a call." and they go off without the re-booking. But if some one said to me, "If you enjoyed your appointment today, would you like to make another booking now on a day that is convenient to you?" ... I would be far more inclined out of sheer politeness to make the booking then and there rather than let you think I had not enjoyed the treatment. It is a subtle approach rather than being so direct. These things do work as most people do not want to offend. The client could still say, "I don't have my diary with me I'll give you a call", but she/he is less likely to! Get what I mean?
Another approach that is good is to offer the client an incentive to make the booking that day ... say a 2.00 saving (NEVER use the word discount ... it is not professional to discount) on the treatment if she books and keeps the appointment she books with you today! That sort of regularity deserves a reward!!
I offer 10% discount if a client re books within 4 weeks, only if they re book before they leave though.
it means i know where i stand with my appointments. I like tolook at my book and see its all booked up, rather than wait around for walk ins.