Liquidity of a market affects the performance of scalping. Each product within the market receives different spread, due to popularity differentials. The more liquid the markets and the products are, the tighter the spreads are. Scalpers like to trade in a more liquid market since they can make thousands of trades a day to add up their small profits offered on each trade.
If they are to trade in less liquid markets, they will try to cover their risks by widening their bid and ask prices.
Volatility
Unlike momentum traders, scalpers like stable or silent products. Imagine if its price does not move all day, scalpers can profit all day simply by placing their orders on the same bid and ask, making hundreds or thousands of trades. They do not need to worry about sudden price changes.
Time frame
Scalpers operate on a very short time frame, looking to profit from market waves that are sometimes too small to be seen even on the one minute chart. This maximizes the number of moves during the day that the scalper can use to make a profit.
Risk management
Rather than looking for one big trade, the way a swing trader might, the scalper looks for hundreds of small profits throughout the day. In this process the scalper might also take hundreds of small losses during the same time period. For this reason a scalper must have very strict risk management never allowing a loss to accumulate against him.