I have an issue whereby a product cost was changed without any adjustments, transfers or receipts having being received.

The only way I can see that the cost would have been changed is by editing the item. There is only one person who has access rights to edit items and this person who is the one that discovered the error indicates that no change was made. The error affects about 5 items.

What are the ways in which an item cost can be changed?
Is there a way to limit changes to an item to simply creating the item, setting location and no access to cost?