I work for Amex. Companies like PayPal, Square, and others have master merchant accounts set up with Amex. Individuals can set up merchant accounts through those "aggregator" companies to be able to accept Amex cards for payment. Most of these types of accounts are for smaller, online retailers or smaller shops. You see them a lot at art shows, flea markets, farmers markets, etc. You might see a charge on your account such as Mark PayPal *Partsplus. Sometimes the "sub-merchant" name matches the location where you purchased your item, while others are generic numbers (e.g. Mark PayPal *YD3896). It can be confusing sometimes and often the charge might be delayed a day or two from when you made the transaction. In a nutshell, many retailers use third-party aggregators to process their charges because it allows them to maintain a single relationship with the aggregator rather than have processing accounts for each card provider. In general, these are legitimate accounts; however, we do see them used for fraud quite regularly, so it's good to keep your eye's opened.
