Accepted solutions (answers which are marked as solving the question) are the perfect way for visitors to quickly find what they’re looking for.
A member posts a question, gets a bunch of responses and marks the one which solved their problem (or an admin marks the best answer).
The problem, like customer reviews, is few people take the time to say if the answer solved their problem. This means most visitors don’t know which (if any) of the responses solved the problem. Most communities are lucky if 1 in 5 questions are marked as an accepted solution (rejected solutions would also be interesting).
You can pester the person who posted the question with pop-ups, emails, and direct messages to mark an answer as an ‘accepted solution’. This might increase the numbers a little. But there is only so much pestering you can do before you’re seen as a pest.
One solution is to enable all members, not just the original poster, highlight if an answer worked for them. This helps a little. But beware the natural curve here.
If you’re measuring (or measured by) the percentage of questions with an accepted solution, after a while, most of the common questions already have an accepted solution. Members don’t need to ask these question anymore. Newer questions are less likely to have a feasible solution.
Another alternative is the ‘best answer’ or ‘featured answer’. These are a little different.
You might not know if the answer solved the problem, but members, volunteers, and admins can highlight which answer they think is best from the ones given. This helps visitors quickly try the best answers before moving on.
I’d measure and work to improve three things:
1) % of questions with an answer (even explaining there is no known solution helps the member move on).
2) % of questions with a ‘featured/best answer’ (set fairly rigid criteria for what qualifies as a ‘featured answer’. This might be it offers something new, something of unique value etc…it might not be the solution, but it’s an answer that offers help.
3) Time to get a featured/best answer. The quicker the answer, the better.
Ideally, every answer would have an accepted solution. Realistically, there are innate difficulties to make that happen. A better approach is to look at a metric you can influence and improve.