Are the Dell Vostro memory upgrades sold in ebay legitimate?

I am planning to upgrade the memory for my Dell Vostro 1400. I found some good deals in ebay. Are they genuine?? Should I buy from ebay or I should always buy from dell??Are the Dell Vostro memory upgrades sold in ebay legitimate?I would check the feedback of those who are selling the product. Usually people tend to sell the same things over and over so in the feedback you can see if someone else bought the same item and were happy with it. I never buy anything from ebay without going through their feedback.