A few people have posted here and on other sites that they were banned from shopping online at Target .com. Asked why, and Target pointed them to just read their Terms and Conditions. Some of these people suggested Target accused them of being "resellers," people who buy certain items (often limited editions or loss leaders) to resell on eBay, gift card sites, etc., who therefore deprive other shoppers of the opportunity to purchase those items and Target of profit on other items that shoppers might usually pick up along with those items. Apparently, Target had a big problem with resellers buying out their limited collaboration with Lilly Pulitzer last year.
They can still shop in stores, but that removes their ability to trick the website to give them the Red Card 5% discount on their entire purchase amount even when using gift cards to pay. In stores, the 5% discount only applies to the amount actually charged on the Red Card.
No one knows what triggers a ban, but it's likely a combination of high amounts and high frequency in a short period of time. A lady who reported her ban here last month said she bought over $25,000+ Disney gift cards in something like a 3 month period. She didn't seem to have done much churning. I think another man who reported his ban on another site said he bought several thousand $ worth of Disney gift cards in a few days and added he hadn't had his Red Card open for very long.