I see this phenomenon in online stores (especially Amazon) that allow users to ask questions of prior buyers. Some of the buyers respond with answers of the form, "Sorry, can't help", "I don't know", or "I'm not sure"

It's not uncommon for askers to append "Don't answer if you don't know" to their question.

Why do people publish content-free answers instead of ignoring the question? What could be done to reduce this behavior?

(Don't answer if you don't know.)

  • 1
    About your last sentence, ironically, “I don't know” would answer your question by showing what exactly happens with answers like that on a website which figured how to deal with useless answers. Sep 8, 2018 at 9:05
  • 1
    Have you considered that some of these useless answers are from trolls or do you only want answers about well-meaning users?
    – zero298
    Sep 8, 2018 at 16:57
  • @zero298 consider trolling to be out of the scope of the question. Sep 10, 2018 at 4:04

2 Answers 2


If you ask this question, I suppose you're among the happy persons who have never read comments on YouTube or any social media.


  • Users are encouraged to contribute (no matter how, would it be by gaining reputation/points, or receiving an e-mail “Hey, there is someone who needs your help on an article you purchased recently,” or anything else),

  • They do not have a direct and clear feedback that unhelpful comments are not welcome,

they would put comments even when they have nothing to say.

Therefore, in order to avoid useless answers:

  1. Reduce the positive effect of any answer,

  2. Increase the negative effect of a bad answer.

Example 1

Here's an example I know well, being an active contributor: Google Maps. On Google Maps, you can post photos of touristic locations. When you post a photo, you receive:

  • An immediate reward—the points you accumulate by contributing to the system, and a very nice message thanking you for your contribution.
  • A long-term reward in a form of e-mails from Google, telling how much you contributed and how much persons have seen your photos.

What happens when you post a photo of a wrong location, or a low quality photo or a photo of your child/cat/whatever?

  • Possibly, someone, someday, will flag it, and it will be removed. I'm not sure you are notified that your photo was removed; possibly not.

Even worse, if you post a photo of a landmark for which there are already hundreds of photos better than yours, you still get the incentive, while taking no risks of getting a negative feedback of your photo being potentially removed.

This creates a strong incentive to post photos, good or bad. And so, every popular landmark is filled with hundreds of photos which are terrible and don't bring anything to Google Maps, or plainly wrong.

Example 2

Now take Stack Exchange. When you post an answer, if and only if the answer is good, you get:

  • The incentive in a form of reputation points.

If the answer is useless, you get a clear and direct feedback which can take three forms:

  • Negative comments.
  • Reputation going down.
  • Your answer quickly deleted.

This makes the user think twice before posting something. The system is not flawless (especially on Stack Overflow, being the most popular and attracting a lot of new users), but even there, you never get totally useless answers staying without negative feedback for a long time.

  • You're correct about me happily ignoring social media comments. Sep 10, 2018 at 4:02

You could do some validation on the text people want to submit. For example if the entered text is "I don't know", display an error message saying answers should be helpful. Basically gather useless generic answers in a database, detect them and block them.

Not entirely the same but I have seen examples of forums that detected if you used all caps, saying they don't appreciate shouting. It was funny but effective.

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