It seems that freelancers coming here are not keen to mark the correct answer. The result is that so many questions is unanswered, while in reality almost all of them had been answered.
What can be done to resolve this?
First, checking the site stats on Area51, we are good in the following areas:
We need to work on getting more active users and visitors (voting, asking questions, providing answers, editing, etc) around to keep it sustained. We are averaging just under 1 new question a day, which definitely needs some work.
I'm personally impressed at how many questions are being answered, just not so many that are being marked as answered. Checking out how many are unanswered is great (only 7, but 5 don't have any answers), and it seems people come, get their question answered, and leave.
Would a contest help? Would a blog help? Perhaps. But I also see lots of low quality answers that don't give much detail, and rely on the person to either look elsewhere, or Google further for their answer. I think if we can improve some of the lower quality (i.e. 1 or 2 sentence) answers, that we can show we are all professionals, and know what we're talking about. Maybe having the people who answer lots, also ask some questions that they already know the answer to, just to keep the community growing.
With all that said, let's remember that this is my first Beta that I started from scratch in, and I have seen it grow nicely in the beginning. My main site after this is Superuser, which has many, many, many more users, so this may be inaccurate, but it's what I see.
When people ask questions, they are already prompted to accept an answer when they upvote one, but people may seem to think that the definitive answer to a subject is the one that should be marked as accepted.
On Stack Exchange, this isn't the case; an asker can mark whichever answer helped as accepted.
The beauty of Stack Exchange is that the best answers will always rise to the top.
Maybe we could try and focus on user retention, rather than just encouraging users to accept answers?
It seems like we're getting a large number of hit-and-run questions from people new to Stack Exchange; retaining them with a more active community might lead to them reading the about page in more detail, or getting to know the Stack Exchange model a bit better.
The key approach is in just continuing to build great content. For every question that is about a real problem someone faces, there are perhaps tens of hundreds of people who will google for that same problem and land on our site.
A healthy Stack Exchange site gets about 90% of its traffic from search engines, which means 90% of the visits are likely to be people who aren't part of the community. Most folks won't have Stack Exchange accounts. As we build more content, we'll get more visitors, and more people will eventually join the community because they'll be naturally attracted to it by the great content.
To get the word out, I regularly tweet interesting questions and post links to them on Reddit. If all of the folks in our community do this and make sure we stay true to the Stack Exchange mission to make the Internet a better place, this site will succeed.
As for the lack of green checkmarks. While it's good you bring it up, it has no bearing on our success. All it really means is "this is the answer that helped the original poster". But considering the tens of hundreds of people coming from Google, they might choose a different solution to help them, so we're still providing a valuable service even if it's not immediately clear what worked for the asker. Hope this helps.