By default, when an Item is unavailable, it will show up in your store grayed out, sometimes with an overlay that says "Sold Out" or "Unavailable" (see the picture below for an example). You can choose instead to display a custom image, called a Sold Out Overlay Image. Often this will be a custom image of your company logo or an item in your inventory, but with the image grayed out and with text overlaid over the foreground that says something like "Please call us at (company phone number) to book this item" (again, see the picture below for an example). Instructions for how to set up a Sold Out Overlay Image are below the picture.
To set up a Sold Out Overlay Image, first navigate to Admin>Website>General Images>Sold Out Overlay Image. If, when you get to Admin>Website>General Images, you don't see an entry called Sold Out Overlay Image, reach out to Tech Support and ask them to add one for you. Go ahead and upload the image into your folder by clicking to the right of where it says "Picture" and then click "Submit."
Next, go to Admin>Order Config>Misc Order Settings>Sold Out Items Opaque, check the box, and scroll down to the bottom of the page and click "Save."
Don't forget to test! You can go to the front end of your folder, choose a date and time for your order where you know a certain item is unavailable during that time, then navigate to that item's Category webpage in the Store to observe your new Sold Out Overlay Image in action.