You need a certain Agility to steal a certain amount of items from a certain store. Stores in Silajam have the lowest requirement.
If you steal the item uncaught, you can continue doing it to get caught. But if it's too low, they won't let you do anything.
After they punish you once, they're gonna watch you closely, so you won't be able to do any stealing.
More specific info: https://tales-of-androgyny.fandom.com/wiki/Items/Stealing