Well, as I only have a few dvd anime dvd's (2 Rurouni Kenshin from the Rurouni Arc, the Legend of Kyoto boxed set, and volume 3 of Cowboy Bebop), I can't really say. XD I had watched (or at least known the story of) all three of those before I bought them, so I was pretty familiar with everything. However, since I buy manga more often (LIMITED BUDGET'D!), I've made several purchases based on reccommendations. Before making a purchase, I do one or more of the following:
~ Read the review here at CAA.
~ If there's not a review, I'll ask about the manga/anime in a thread.
~ I'll read others' thoughts about the particular series, and see if it appeals to me.
~ Sometimes, I'll be able to borrow a few volumes from a friend, and then I can see whether or not I'll enjoy it without risking a purchase that I won't be happy with.
Content is probably the most important thing to me when I'm buying anime...I don't want to buy something that I feel like I have to hide from my parents or anything. XD I wouldn't be half as dissapointed about a boring series I bought than I would be about a series that I would have to hide.