How the heck are you able to get this data? I called the local store (Fred Myer) and they say they don't know they wait until the truck arrives and then they see what they get.
- track what users are searching for in an area (e.g. toilet paper)
- use GPS to determine who is at a store nearby that hasn't had that item updated recently
- prompt the user via notification with something like "Does [grocery store you're in] have toilet paper in stock?"
Admittedly it's not motivating anyone to answer, but it might help to keep data fresh.
But with many users, notifying other people will just make the store run out of stock sooner. So people will revert to texting their friends to let them know when something's in stock.