As a rule, I can hold an item for you if needed but it depends where I’m selling.
If you meet me at a trade fair like Hellocon I can hold the item for a couple of hours but not the whole event especially if the item seems popular. If you contact me when I’m not at an event (or the item isn’t with me at the event) I can hold items couple of days or weeks. Remember to ask because most of the time I can hold any item as long as needed.