Yep! I've noticed older games tend to utilize this trick; I spotted it in a certain Korean golf MMO from ~2004. It did have me scratching my head initially, but if I were the one designing the game, it definitely would've occurred to me that I don't want the value to mismatch. Of course, I think this is a bit old-timey now. If I were developing a game today, I'd probably make the store emulate how a typical store with a shopping cart works; do everything on the server side, and just display it to the client. I can, however, imagine coming up with this scheme if I were faced with the same problem, and I can appreciate that it is an elegant way to reduce the load/statefulness of the server without adding the risk that someone might get shafted.