Dynamic Weapon Pricing (sometimes referred as the Weapons Market) was a major overhaul to Counter-Strike: Source and its weapon pricing that came out in October 11, 2006. It sparked controversy among fans and since been removed due to strong opposition.
Each Monday, the prices of weapons and equipment would change depending on how much they were used that week. (Example: if 10% of all dollars world-wide were spent on the Maverick M4A1 Carbine, then its price will increase by 10%.) It was a system of basic supply and demand.
Each week, the total number of weapons purchased world-wide since the previous week's change is counted. The purchase data is gathered directly from game servers. Every 24 hours, game servers would upload a file to Steam and list the quantities of all items purchased over the course of the previous day.
The main problem with the Dynamic Weapon Pricing system is that it made difficult-to-use guns underused whilst promoting normally lesser used spray-and-pray guns such as SMGs. While decreasing the price of a MAC-10 to $140 increased its usage, the accurate rifles that took more skill to master became less used. This eventually led to more people using guns that are easier to use which went against the competitive nature of Counter-Strike and hence, making dynamic weapon pricing wildly unpopular.
Under this system, certain guns were almost impossible to be purchased or made completely impractical. For example, a Desert Eagle usually had cost more than $5000, making it more expensive than an AWP. It also meant that not only it was unavailable for pistol rounds, it was also a pointless purchase later on and almost impossible to buy if on the losing team. Additionally, the Scout would usually cost more than twice the price of an AWP due to it being normally less used, making it completely impractical due to it being more expensive and being weaker than the AWP.
The change was heavily criticized by the community and swiftly removed a few months after its introduction.