I get people looking then coming back all the time, there is so much competition with jewellery. When they ask for a hold, I will only hold for an hour, and I ask for their name. Since I started asking for a name, I find that 99% come back, even if just to tell me that they changed their mind, though 90% still buy the item they put on hold.
If they want customization (example if I need to change a bead on an earring), then they must pay first, and can come back to pick it up later. I no longer will waste my time while set up at a show sizing or customizing without payment, because that time could be spent making something else, or just talking and selling.