Someone needs to take all the OBD2 scanners out of the part stores and throw them in the trash. I see it time and time again where dumb ass behind the counter sells customer wrong part because of a trouble code stored in the vehicle. 99% of the employees that work in these stores including store managers, their boss, and their bosses boss do not understand why the light could be setting.
I can not count on my hands the number of times I had to stop someome from behind the counter who could possibly be selling someone the wrong part based on a check engine light code. Yes I did spend a number of years working at Auto Zone when I had the dyno in the beginning years. Customers are expecting the parts they are purchasing to fixed their problem. They do not want to come back with a check engine light on after the 10 dollar an hour counter guy told them the part they purchase would fix their problem.
Offering to scan vehicles for a check engine light is a mistake in my opinion on a store level. It may look good to all the bean counters at the top of the food chain when in fact they do not even know what Long Term or Short Term Fuel Trims mean.
Long story short. Please educate your customers that a part is not always going to fixed their check engine light.