Here is an example script that looks for an item specific called “Material”, and changes the selected listing name to include its value
tell application "GarageSale"
repeat with theListing in (get selected ebay listings)
repeat with specific in item specifics of theListing
if the specific name of specific is "Material" then
set materialName to item 1 of (get values of specific)
set listingName to "my listing title " & materialName
set the title of theListing to listingName