We aren't allowed to post an official list of authorized download vendors (I don't know why), but Bigtaxdeal is not one, no legit authorized seller would use PayPal, and no legitimate seller uses Dropbox, GoogleDocs, or other consumer-level file servers to deliver the download.
You will have to seek recovery from PayPal. We will report the unauthorized reseller but if they are overseas they may be difficult to block (maybe Security can de-monetize them by getting their PayPal canceled.)
We can't help you verify if the software is valid and not tampered with. We recommend you delete the download and re-purchase Turbotax from an authorized vendor like Costco, Amazon, or Staples.
