I'll try and keep it short
People give their own opinion and the person asking decide themselves what to believe/make out of the information they received, end of story.
Sounds good but the people requesting advice are ignorant of the price or they wouldn't be asking. The people that are responding are presumed somewhat of an authority (they at least no more than the requester) so there is the implied trust that the information given is somewhat accurate. I'm saying that the information is nowhere near accurate enough to honestly put forward. You're asking people to decide if they should believe an answer to a question they asked. I hope you can see how that's a problem.
"This price check may or may not reflect the current market, so keep in mind that the suggested prices may or may not be reached if you do decide to sell/buy the item."
If you have to apply that warning like that then you are conceding the numbers given are basically worthless (which they are). So why bother having them at all?