If a user keeps posting poor answers to your questions such as because skimming the question, is the best action to take to downvote or is there some way to prevent it? I don't like when that happens because it makes the question look answered. I feel bad about downvoting someone so if I do downvote, I wait until they get a +1 (if they do at all), but maybe I shouldn't feel that way (perhaps I'm the only one haha)?
Discourage bad answers by downvoting them. Don't wait until they have an upvote left by someone else, as this is a net gain for the answerer and will only encourage them further. And if the answer is truly bad, it should not be getting upvotes!
You should also comment to explain why the answer is bad. For instance, explain what details from the question they missed, or any other significant problem with the answer.
Wrong answers normally should not be flagged for moderator attention, as it's also possible to learn (e.g. what not to do) from wrong answers. The big exception is if they are harmful or malicious. For instance, if someone posts an obfuscated command that would result in data loss if someone ran it, that would be something we would want to nuke on sight (and this has happened).
If your question is getting a lot of bad answers, though, it's a strong indication that the question itself is the problem, and should be edited to clarify and improve it.
No, you can't, and that's a very good thing.
- You can always downvote an answer.
- One answer will not stop others from reading the question and contribute better answers if they feel that the present one is not good enough.
- If really necessary, you can flag for mod attention. But this shouldn't be done for lackluster answers, only for real bad stuff (even for plain wrong answers, a downvote and maybe a comment why it's bad would be sufficient).
Some further thoughts:
First, the negative impact you fear is either extremely small or non-existant anyway. Second, after having read the conditions you added to your bounty question I have to say I dislike your attitude. SF is free for everyone and you just don't get to choose who, how or what people answer. If a partial answer contributes to solving your problem, you should be thankful for this, and even if it is wrong, someone took the time to try to help you. Be grateful! And adding 100 worthless fake internet points to your question still entitles you to nothing!