There are a number of ebay sellers that do sell nice wigs. I personally like buying from Fantasy Sheep [buying direct off their taobao site is cheaper], Laura Wu, Cosplay Wig, Epic, and Wigs-us.com [not ebay but a nice place for basic, natural wigs]. Quality depends on what you buy. I have no trouble with any long wigs I have purchased from any of the aforementioned places and their photos are pretty color-accurate.
Here is a helpful reference [apologizing ahead of time, it is a wide image that will break frame but you still want to read it]