1) Votes cannot be bought by a lobby since they would have to pay off each and every citizen.
On many issues, it can be just as easy to buy a vote. If current polls show a split of 45%-55% for an issue, those who want to buy the election just have to change the opinions of 6%. An ad campaign of some sort can do that. Remember that they only aim to change the "swing" votes - they don't need to worry about the opinions of those that are strongly one way or the other. Maybe it is more expensive in some cases, but still very plausible.
"My sense of purpose is gone! I have no idea who I AM!" "Oh, my God... You've.. You've turned him into a DEMOCRAT!" -- Doonesbury