There is a known halacha that one shouldn't eat in a non-kosher resteraunt due to Maaras Ayin, even though they serve kosher food also.
What defines a non-Kosher restaurant?
McDonald's is probably the most famous non-kosher restaurant out there.
What about Starbucks? There are kosher Starbucks drinks, and non-kosher Starbucks food. Yet the cRc allows drinking (kosher) Starbucks beverages.
7-11 has kosher and non-kosher food.
What's the difference between McDonald's, Starbucks and 7-11?