I didn't mention the employee's name for a loooooong time - figured it would give them time to clean up their act, and I don't want to see anyone fired.Report her to the store manager. If she remains there still, call corporate and let them know what's up.
BUT
After the 3rd time, whenever I talked to the manger I'm immediately referred to said employee - I tell them "well, your employee is the problem".
BTW - the 3rd time I caught them, a former co-worker had just asked her about 22 ammo, and was told they were out. We were standing at the end of the aisle when I spotted one of the "insiders" from across the store making a beeline towards the sporting goods department.
Figuring something was up, I gave him a second to pass by us and check the counter, then followed him to the counter - the employee was selling him 22, which they had just told my friend they had no more of.
Waddya gonna do...?