Both Hamas and Fatah are corrupt. However, it is impossible to have a free and fair democratic election under an Apartheid State. The Apartheid must end first before it is possible for Palestinians to have a free and fair election.
Hamas does torture and kill political rivals, and has been exposed for corruption. Fatah is also corrupt, seen as working at the behest of Israel at the expense of Palestinians in East Jerusalem and the West Bank.
Both have been funded by Israel as part of a Divide and Conquer tactic. Israel also has a long history of assassinating more moderate and leftist political Palestinian rivals.