Actually a lot of things say they are kosher but are not. The second avenue non kosher deli is an example. In Baltimore there is a place called Lennies. They will grill hotdogs that they say are kosher but as soon as they are taken out of the package and hit the grill that is used with cheese and unkosher meets they cease to be kosher. What I would like to see is a restaurant that is less strict, but still adheres to reasonable laws of kosher. One where customers don't have to pay for someone to sit around and supervise all day, but does not do anything blatantly unkosher like serving ham and cooking milk and meat together.
What makes it not Kosher?
Why are you not allowed to mix Meat with Dairy?
What makes it not kosher?
We are commanded not to "Cook the baby in the mothers milk", according to the Torah.
This has been taught to mean that we cannot cook meat with cheese or milk. It was for several 'reasons' including that it is a merciful thing, because milk is for the babys goodness, not for its death. And also because the Idol worshipping nations would always cook meat with cheese {sorta like Mexican food}.
From Rambams list of Mitzvahs this is Mitzvah # 195
195) Not to eat meat and milk cooked together Ex. 23:19
23:19 The choicest first-fruits of thy land thou shalt bring into the house of the LORD thy God. Thou shalt not seethe a kid in its mother's milk.
There are many good resources which will explain it...
http://www.aish.com/torahportion/livelyparsha/Lively_Parsha_Mishpatim.asp
KEEPING KOSHER
The Torah says: "Do not cook a kid in his mother's milk." These words are found 3 times in the Torah, representing 3 separate prohibitions.
1. Do not cook meat with milk.
2. Do not eat meat cooked with milk. (Yes, including cheeseburgers - oh no!)
3. Do not derive any benefit from meat cooked with milk - even unintentionally!
The reason the Torah uses the words "kid in its mothers milk," is to teach us that even though the main sustenance of the kid is its mothers milk, it is still considered a foreign substance and forbidden to be mixed. Certainly all other milk is forbidden to be cooked with meat.
The Torah's specific wording also limits the prohibition to kosher milk (mother's milk), kosher meat (goat, sheep, cow) and only animals (as opposed to birds). Rabbinic law, however, prohibits all types of meat, and even meat mixed (but not cooked) with milk - since these could easily be confused with the forbidden stuff.
I hope this helps...
muman613