This happens regularly:
- A new user posts their first question
- They get a good answer
- So they leaves a comment saying "OMGz Thx it WORKEDD!!! you have saved my life :D"
- Answerer leaves a comment back saying "You are welcome, but on SO to say thanks we up-vote and accept; do this by clicking the hollow tick mark"
- User doesn't know the SO way of accepting and up-voting, and doesn't see the comment until they need help with the next problem (if at all).
My suggestion is for users with low rep, low questions, low accept rate, if they leave a comment containing some keywords such as solved, worked, or thanks, a dialog box appears with a message similar to:
On stackoverflow.com you show you appreciated by accepting and up-voting, would you like accept this answer?
Accept | Don't accept this answer right now
The answer then gets accepted and +1 (if the user's rep is high enough) if they choose to accept.