I have ordered a bunch of phones before from wirefly. I just got through ordering the S3 from them this afternoon, and my total was $499 flat...no tax or anything.
Shipping takes a little longer than you expect but hey at least you're saving some money.
The only problem I ever had with wirefly was when I ordered my 2nd Esteem, they put the LTE card into it backwards and it took me 30 minutes to realize that...then I called them and complained about this to them and they sent me a free bluetooth headset as an inconvenience. Other than that, never had any problems with any of the phones I got from them.