It is not whether a trader or investor sold or not, it is illegal IMO from reading the following. Read "Bear Raid"
Market manipulation is a deliberate attempt to interfere with the free and fair operation of the market and create artificial, false or misleading appearances with respect to the price of, or market for, a security, commodity or currency.[1] Market manipulation is prohibited in the United States under Section 9(a)(2)[2][3] of the Securities Exchange Act of 1934, and in Australia under Section s 1041A of the Corporations Act 2001. The Act defines market manipulation as transactions which create an artificial price or maintain an artificial price for a tradeable security.
[edit] ExamplesPools: "Agreements, often written, among a group of traders to delegate authority to a single manager to trade in a specific stock for a specific period of time and then to share in the resulting profits or losses."[4]
Churning: "When a trader places both buy and sell orders at about the same price. The increase in activity is intended to attract additional investors, and increase the price."
Runs: "When a group of traders create activity or rumors in order to drive the price of a security up." An example is the Guinness share-trading fraud of the 1980s. In the US, this activity is usually referred to as painting the tape[5]. Runs may also occur when trader(s) are attempting to drive the price of a certain share down, although this is rare.
Ramping (the market): "Actions designed to artificially raise the market price of listed securities and to give the impression of voluminous trading, in order to make a quick profit."[6]
Wash trade: "Selling and repurchasing the same or substantially the same security for the purpose of generating activity and increasing the price"
Bear raid: "Attempting to push the price of a stock down by heavy selling or short selling."[7]
AI
Market Data 
Markets 
