I see the seller will allow return within 7 days after the buyer receives it. So, you would have a chance to try the RAM in your computer and, if it does not work, return it.
As far as price, I have the impression you are not familiar with ebay auctions. The bidding on that item does not close until Sep 10, 201015:38:28 PDT. Bidding near auction close time often occurs at a rapid pace and quickly drives the price up shortly before the auction closes. So, in the end, it's selling price may not be much, or any, less than crucial.com.