I've eaten at Corner Mercantile about 5 times (maybe more) before writing this review.
Staff: Very friendly. Each time I've gone to CM I've been immediately greeted after entering. The general manager is visible, accommodating if you're looking for a certain item and also works the register.
Food: Everything is fresh. From the sandwiches to the vegetable sides to the pastries and the house made iced tea. I try something new every time I go and everything has been great.
Cost: For getting fresh made food that actually is nutritious and filling the value is there. You're probably looking to spend around $10 for lunch.
What you should try: Prime rib sandwich - simple sliced prime rib on a fresh roll with salt. Also, cheesecake!
Overall Corner Mercantile is a great addition to the downtown Pittsburgh breakfast and lunch scene for those looking for quick food that isn't chain fast food.