Believe or Not Believe?

I am working since the new Summer Semester started 1 week ago. And, a lot of thing have been happened when I'm working. Referring to my topic here, believe or not believe. I think you will say, "why and what"...

Here is the point that I want to tell you. We have sell Preserved Egg, but it is out of stock since few weeks ago. One customer has came and asked me where is the preserved egg. I answered directly that it is out of stock. Now, guess what the customer answer to me? She said, "Are you sure it is out of stock?". And I answer her again that, "yes, it has been out of stock for long time already". But then, she go and ask the other sale assistant, who is older and more experience than me. After ask the other sale assistant, then she believe it is out of stock.

Wow!!! Many people DO NOT believe on teenagers like us!!! Customer like this are mostly married, and more than 40. It's not only 1 customer is like this, but MANY!!! I hate them... -.-" Many customer also think that teenagers like us, do not know how to do everything, and treat us do not know anything. My question here, why are they do not believe in us? = /