I've never pressed people for a deposit on the spot. I don't know any professional who actually does. It doesn't inspire confidence and the result is customers who are more difficult to please because they never really arrived at the decision with full conviction and a collaborative intention.
I give people a contract and if they deceide to go forward they have 30 days to perfect it and pay the deposit. This provides them the time they need to check references and arrive at the decision entirely on their own. The result is a client who is fully invested in the choice and is easier to please. No one who booked me in this manner has ever nick-picked my performance - not even when I've made very obvious mistakes.
If they haven't actually declined the offer during the 30 day period I will call them should a conflicting request arise. I've rarely had to do that, because most people will call within days to let me know their intentions,
They can take longer to decide if they want - but after 30 days I would no longer follow up with them regarding competing interest in that date. I can obviously accept the booking after 30 days but the obligation is no longer there if I've already movend onto another customer.
I've also NEVER used a follow up to fraudulently pressure someone into booking (pretending there's another customer when in fact there's none.) This would simply undermine the whole basis for having giving them space.