Interesting. I wouldn't categorize a market that has N customers and 1 vendor, or 1 vendor per type of good (as in this case, since a market could have other types of goods and services not sold by a grocery store), as not a "market". It's not a "competitive market", but since a market is by definition, a place where buyers and sellers exchange goods for money (or goods for goods), then I think it still qualifies as such.