I know this was brought up here previously, but there may be a more viable solution rather than to have this quest never close out if you decide to keep Buddy. I keep buddy and set a Complete Quest at stage 520. All works well with that. Where I feel they went wrong with this quest is if you do not talk to or meet Rufus ahead of time, there is always a dialog option to sell Buddy to him once you finally do. There is a duplicate response in his dialog tree if you already talked to him that could be replaced with this option to sell him. All options would still be there along with this one. This would allow for you to finally close out the quest and still allow for the sale at any time. I'm not skilled enough yet at quests or I would have tried it. The only thing that would probably change is negotiation for price in the current quest tree if you bargained for higher payment. Just a thought if you wanted to look into it again.