Is buywitbit.com an authorized retailer of TurboTax? They came up at the top of my google search in the paid ads section. Is there a way to test a download for malware?

No, they are not authorized to resell TurboTax products. By purchasing and using software from an unauthorized seller, you may expose yourself to risks such as viruses, malware, and/or identity theft.

This seller may be a pirate. For more information about piracy, please see: https://www.intuit.com/legal/piracy/ 

Yes stay away from them. I got bitten. There is no response. It's a scam that TurboTax should take steps to bring them down.