On The Border Desception, Fraud, Theft Saint Charles Illinois

I brought my family to On The Border restaurant in Saint Charles Illinois for Cinco De Mayo.  This is a restaurant we have frequented in the past.

I ordered a house margarita with my meal and the waiter asked if I would like a 12 ounce or 18 ounce margarita.  I ordered the 18 ounce.

I was surprised when the drink arrived in a 16 ounce plastic cup.  The waiter explained to me that because of expected high demand (Cinco De Mayo) they were using plastic cups for margaritas.

I asked the waiter how they get 18 ounces of margarita into a 16 ounce glass.  The waiter stated that the bartenders proved to him that this plastic cup holds the same amount as the normal glass in which margaritas are usually served.  The waiter said that the bartender filled the usual 18 ounce glass and dumped it into the 16 ounce plastic cup.

I brought the plastic cup home and measured that it indeed only hold 16 ounces.  This is also indicated on the bottom of the plastic cup.

So, I have three issues...

1) I ordered and paid for an 18 ounce drink, but received only a 16 ounce drink.

2) I have been to this restaurant many times and paid for many margaritas.  The waiter indicated that the glass used to serve 18 ounce margaritas is only 16 ounces.  

3) If they cheat and lie about the drinks, what else do they cheat and lie about?