I personally have not been banned so I can't from own experience. What I do know is this: Three people I know have been banned. Two were banned from NM for excessive returns (and store CC's account closed). What they were doing was.. purchasing items during SALE EVENTS and working in tandem to buy at the next discount event.
The other is a chronic returner and was banned at Macys, The Limited, and
Coach for excess returns. I believe that she has been reinstated to purchase at The Limited now. But she has not been reinstated at Macys or Coach. I know Macys pretty much told her, to never come back again.
I am close friends with a store manager at another high-end dept store. I know they ban people there for a number of other reasons (other than returns). If they suspect fraud... or suspect money laundering, or make claims of items not received (when system shows received) .... if you use the "employee" discount without being an employee.. (or accept any other discount the store normally does not offer) you may be banned.
I just recalled another friend who was banned from VS for doing the following: taking the customer returns that the store discarded (VS discards used items upon return, even if the beauty product was just opened to be sniffed or when an item comes back without tags attached yet clearly it appears brand new and not used). This was an employee though. She wanted to sue them but the employee handbook clearly stated the type of items that were to be discarded and that
the employees were not allowed to take them. Fired and banned from shopping there.