I took my car to a Valvoline Instant Oil Change in December. They screwed up and cross threaded my filter and the Walmart tech's discovered. Valvoline refused to accept responsibility even though I had proper documentation to prove as well as the filter which appeared to have been forced. I told my local manager of Walmart about the predicament and he said to bring in a reciept for the part and he would handle it. I purchase a lot from Walmart and they are very easy to work with and have never had a bad experience, yet everyone talks about evil Walmart.
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Whenever you're at the top of your respective industry you can expect to be targeted. I find it hypocrital that many will be anti Walmart yet go to Target or Kmart who have had many of the same issue. If you go by a percentage of employees they are no worse than most. They employ so many people you are more likely to hear the stories based on the sheer number of people.

Read about one Target incident:

http://lawinlife.wordpress.com/2007/01/27/target-corporation-settles-racial-discrimination-lawsuit/

Or Kmart:

http://www.detnews.com/2005/business/0507/25/A01-258133.htm

They all do the same thing?