I was looking through the advertising forum and saw all these 25-50% off "sales". When I look through their shops it seems most items are priced normally. I look through the comments and people are talking about trades and messaging. What's going on? How do these sales work?

You have to figure out the percentage off of the current shop price of an item (i.e. an item in the shop that is 10mil and being offered for 50% off would be 5mil.) Then ping (on the forum thread) the user having the sale, and they would take the item out of their shop and put it in a trade reserved for you where you pay the sale price. Hopefully that makes sense! ^^

Oh how interesting. That makes sense. Thank you for explaining. I like that it gives people an excuse to browse and others can move slow-to-sell items.