The laws vary by state, but heres a good synopsis:
The stores have a right to ask, but they have NO RIGHT to force you to provide them with the receipt or detain you for not showing it. If they witnessed me pick up the item, and try to walk out without paying they could detain me on suspicion of shoplifting, however if I paid for my item, and them go to leave the store with it, the do NOT have a legal right to demand I show them a receipt or to detain me under shopkeeper exhemptions to the false imprisonment laws.
The key paragraph is the synopsis at the bottom:
Litigious customers facing off against the police or Costco might not have much luck. Police need probable cause to conduct a search, and Costco members have voluntarily agreed to submit to searches. The question of law is more interesting when a retailer like Circuit City attempts to implement a receipt-check policy without the benefit of a member agreement. In states where the shopkeeper’s privilege exists, stores like Circuit City may only claim the privilege to search customers when the store agent has a reasonable belief that a customer has engaged in unlawful activity. It seems implausible that store agents could honestly claim they need to check every receipt on the grounds that they have a reasonable belief that every one of their customers is a thief.
As I stated before, Wal Mart has a right to ask, and you have a right to obligue or not. However simply refusing to obligue the request is NOT eviden or justification for them to suspect you of being a theif in and of itself and detaining you for refusing would indeed put them in violation of false imprisonment statutes.
Now if they witnessed you not try to pay for the item and try to walk out with it they could detain you, but simply refusing to produce a receipt is NOT legal grounds that will meet the shopkeepers exceptions to unlawful imprisonment. Every state has varying laws, so double check, but in general the simple act of refusing to show a receipt does NOT give the store any right to detain you.
I ran across that site in my search.
I was hoping for a statute or court decision, neither of which I have found.
Thanks anyway.