I'm strictly speaking of oligarchy in the sense Polybius used it: rule of the few. Whether came from money, military success, good looks, brains, whatever doesn't matter. To put it differently, if there were a small number of wealthy citizens who had no political ambitions for themselves or others and the magistrates were chosen by lottery, it wouldn't be an oligarchy--1. it would be rule by the many. If everyone were equally rich, but only 10 hereditary families controlled all the offices of the state--it would be an oligarchy. 2. Thus, the definition of oligarchy is independent of economic control.
1. No, it would be rule by lottery. 2. Economic control is the essence of oligarchy.
Were voters sometimes bribed? Our sources certainly say so. But I think one has to question what's really going on with these bribes. The fact is that the ballot was secret. Thus, a voter might be paid to vote for Bibulus, yet vote for Caesar, or vice-versa, and no one would know or get their money back. Moreover, there were laws against bribery, courts devoted to prosecuting it, and elections entirely annulled because of the scandal of bribery. Finally, and I think this is a critical question to ask: if votes did not matter, 1. why did anyone want to buy them? If Rome were a hereditary monarchy, votes would be worthless and no one would care to buy them. Doesn't this suggest that the votes of the people really did count for a whole lot??
Then, why did they?
Please don't misunderstand me: I'm not claiming that the Roman republic was a democracy, nor that it was a utopia, nor that the civil rights of the people were never violated during the long history of the Republic. My claim is that Rome had real democratic elements and that it's incorrect to call Rome an oligarchy. In contrast, a system of hereditary rule by a single extended family through their appointed magistrates--that IS an oligarchic system, and it was the one that was in place during the principate.
What would you call the Republic?
You have an excellent thread going here, and we all shall learn much from your erudition. I feel that its applications to today are very important.