How do I measure a user’s seriousness while filling an online form?

I'm going to measure a user's seriousness while filling a form. One example of a way to do this is with a time calculation from when the survey starts until it is submitted. By considering this time, we can eliminate some users who finish the survey too quickly. I might also record the user actions (clicks and mouse movements) along with the time stamp while answering the questions.

I need to eliminate the users who will submit the form without providing serious answers. Are there any techniques to measure a user's seriousness while completing a form?

Limitations:

• Calculation can be done until the user clicks the submit button.
• We are not considering the answers.

User Seriousness

Some users are filling the form without understanding or reading the questions properly. They just fill it.

Questions can be single choice questions, multiple choice questions, open ended questions and etc.