Went to blockbuster.com and found the details:
Rent It! Like It! Buy It!
Price excludes tax. When you rent a select promotional title (titles determined by Blockbuster) on DVD at this store location, you can purchase one (1) previously rented DVD copy of the same title for just $9.99 plus tax! Both the rental and purchase must occur at this store location. The original receipt (no copies) showing the rental of the promotional title must be presented at time of purchase to receive the promotional price and promotional price only applies to a purchase on the same BLOCKBUSTER® membership account as the rental. This offer is not transferable. Promotional price can not be combined with any other discount or offer. Promotional price cannot be applied to any other title. Previously rented copies are limited in quantity and only available while supplies last. There may be a substantial delay between the release of a title and its availability as previously rented product. Membership rules apply for rental. Offer valid for a limited time. See receipt for applicable rental promotion dates and expiration date of promotional price.
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IIRC, Blockbuster was going to a "Pan and Scan only" policy, so good luck finding a WS version to rent. It looks like they will only sell you a used one ("previously viewed").
The website does list the WS version, but I don't know what the ratio of P&S vs WS is in the Blockbuster retail brick and mortar channel.
I haven't been to a Blockbuster in years, so I don't know what the rental price is, either.
Still, sounds like a good deal if you can get a scratch-free, complete in box used WS version...