I recently purchased a White Opaque Halfmoon from Aquabid with no trouble. Aquabid is like any e-commerce site in that you just have to be careful of what sellers you buy from- So make sure to check the legitimacy and reviews left on any seller you're considering buying from. (I highly recommend GreatBettas, very fast service.) Also, remember that the Express Mail Transhipper Fee, Airmail shipping fee (from the breeder), and a $20 fish price can total $50-$70. If the fish has rarer markings or green coloration, it's typically $10-$20 higher.
I personally recommend buying from AquaBid over other online websites, because you're buying from individual breeders or small companies. This means that you'll get faster service and less errors if you buy from a good breeder. http://LiveAquiria.com
is a another great site for buying live fish including Bettas, but you don't have the selection that AquaBid offers.
The last thing to consider about AquaBid is that alot of breeders aren't located in the USA. This means that you'll have to payer the buyer's preferred transhipper individually.
Good luck! :)