So even with the price, can we still put (PM us for  Best price, or PM for nego and  etc), depending on the requirements? Well, placing price is just an first level understanding, where  MOST of them can be placed, hence there is what we called as  SRP (Suggested Retail Price)

Assuming that we take an phone for example, Samsung Galaxy S7 Edge, SRP 3k. Sample below
SRP of  most goods are widely available (Especially laptops and etc), by implementing price requirements, it will help a lot, but for those who still plays the same game as above (For the sample above), they will be losing potential customers that  is looking for a faster deal, then to wait for someone's PM.

Nevertheless, +1 for TS's request

Well such posts aren't breaking any forum rules.

I still don't understand why people can be so lazy to "PM best price"

If I want the product, I will PM the seller and negotiate rather than requesting the seller to PM me.