After an item is sold instead of DELETE from the store it is better for SEO to leave it there, but then you can't DISABLE or HIDE it (it will be invisible to the public). So will your X-Gallery work like this: after sold, transfer it to the gallery by changing the CATEGORY from "STORE ITEMS" to "GALLERY ITEMS" (those are custom labels) and also to remove all the labels that a visitor would associate (confuse) this item with a store stock item, such as (take a look at the attached screenshot):
REMOVE or rather REPLACE:
1. PRODUCTS label replace with EXHIBITS label
2. PRODUCT CODE: replace with "GALLERY CODE" label
3. "Set your own price" text replace with "custom label text" or REMOVE it
4. "Set your own price! The price for this product...." - REMOVE or REPLACE with custom text of my own
5. "Out of stock" label replace with custom label or REMOVE it.
6. If possible without an unreasonable cost involved to include a Google Adsense banner (any banner) on the final enlarged pop-up that displays the exhibit/product in its maximum size.
X-Cart Ancient - 4.1.9
X-Cart Gold - 4.7.12
Windows 8.1 and none beyond