I'm torn about this place. It came highly recommended from a local Vietnamese person and other Yelpers. Sadly, I am spoiled from growing up in Orange County, CA, Little Saigon - where Vietnamese food is amazing.
Ben Thanh is a bit more upscale in service than most casual Vietnamese restaurants. Their prices are also higher than I'm accustomed to, but that may be because there aren't a lot of good Vietnamese restaurants in Charlotte (at least none that I've found yet).
We ordered the vermicelli, pork and egg rolls. The flavors were right, but the portion was pretty small. Not enough noodles or veggies. I think it cost around $8+, which really should buy you the same dish plus shrimp elsewhere.
It's fairly authentic, but don't take it as the standard for Vietnamese food. There are a lot of restaurants in SoCal that will have you craving it every day. This is not that level of a restaurant, but OK for Charlotte. If it were in SoCal, I'd give it two stars.