Getting lunch downtown is not always enjoyable. With the same few mediocre chain restaurants glutting the market (Au Bon Pain, Subway, etc.) it's easy to fall in to a rut.
Enter Istanbul Grille:
The portions are generous. The prices are fair. The staff is friendly and personable. The food is excellent.
I, too, tried to pay with a card my first time there and also was told I could pay next time. When I offered the cash I did have (a $5 bill) the guy behind the counter refused to take it so I just tossed it in the tip jar. That's how you build a loyal customer base.
Note to first-timers: The ordering process is a little confusing so either go with someone who's been before (if you're the type who doesn't like seeming like a newbie around the regulars) or be prepared to ask a few questions. And try everything because it's all terrific.