So I went and bought an item at 240 CSC. But after I bought it, the same, identical item went up to 400 CSC. Why?

If people put two of the same item in there it will stack and only show you the cheapest price. If you bought one of two and there was only one left in the shop, it could raise the price of the remaining one.

Alright, that makes sense, thanks for answering :)