We sell shirts to donors using a shop form and use the "maximum # of items to purchase" feature to limit sales to what we have in inventory. When we re-stock an item, we can't just update this number to the inventory on hand because the system recognizes previous purchases and decrements those from the number we enter (e.g. if we enter 10, sell those 10, then re-stock with 25 and enter 25 in the field, the system will only display 15 available for purchase... 25 entered in the max items field less the 10 previously sold).
The only work-arounds right now are:
1) make a new item with the re-stocked quantity--this clutters the shop screen, confusing donors & making sales data messy; or
2) clone the shop form and edit the quantities of all items--this takes significant work, creates multiple forms, creates many opportunities for error, and makes analysis of sales more complicated.
We haven't tried deleting the sold-out items and creating a new one because we're afraid of losing the historical sales information.