In this case the forum is the market, so perhaps forum members should be able to chime in that something is priced too high. IMO (and again it is just my opinion) the information in your example should be allowed and then the buyer can decide whether the price difference is warranted.
I would respectfully disagree. Unless the OP is a noob, it is sufficient to let the market work. If the item does not sell, the seller can choose to lower the price or withdraw the item. If someone wishes to pm a lower offer, that is between seller and proposed buyer. I have pm'ed lower bids and have had them both rejected and accepted. Seller's option.
And, of course, the person suggesting the priceis too may simply be wrong or mean or vengeful or an attention slut - there is just no way of knowing.
I would further submit that pointing out that you think that the price is too high hurts the seller. It may be that the seller is posting an item that i really, really want. I might be willing to pay a premium because I really, really want it. However, a post that the price is too high might cause me to wait to see if the seller takes the bait and drops the price. I say, let the market work its magic.