This is a great question because with microfiber catching on, people can pretty much go to any store now and find microfiber. Does this mean it's good quality? Not always. Usually, and I stress usually, low quality microfiber towels will be 12 by 12 in size or somwhere in that range. While they feel very soft new, they don't after numerous washings. Here's a little test that I've done, and you can do it too:
Take your microfiber towel and get it wet with water. Ring it out until it's damp and hold it up to a light source being a window, a flashlight or whatever. Look to see how much you can see through the towel and compare this with other towels. It has been my experience that the cheaper the towel, the more you can see through it. This tells me that cheaper towels have less thread count, or are not as plush as the better made towels.
When I first started buying microfiber I really had no clue what it was all about. I started using microfiber from Walmart. While it worked ok, I noticed marring and linting from the towels. I began to research more about microfiber and I realized that not all microfiber is the same. I would say that if you go with pretty much any quality vendor, you will have good quality microfiber. Does this mean that you can't get good quality from a local store? No, but be careful.