I'm not on a disposable income, so it's reasonable to understand that I can't buy everything at once. So if I'm interested in something you're offering, I will contact you and let you know and give you a time frame on when I'd be able to get it. I also understand if you say you're not willing to hold it.
But please don't say you'll hold an item, and then back out on me. The worst I will do is tell you I need more time, I won't ask you to hold something and then back out on you.