1. it can be because of fundamentals causing a shift in supply, price increase, sellers increase while buyers decrease.
2. it can be because during a transaction of shares being traded, when sellers meet buyers, the price being traded is always higher than market value.
Theres many more explanations, but thats all I could think of for now....a bit blank atm.
This is impossible. For there to be a seller, there must be a buyer. i.e. It is impossible for more shares to be sold than bought.
There may be more "individual" sellers than buyers, and this infers that the buyers are buying bigger parcels than the sellers are selling, but the actual number of shares must be the same.