Markets fluctuate and that would not be a reflection of current reality. Sometimes the market on something accelerates beyond expectations in a short time, then a new supply is found that suddenly takes a unobtainium peice and makes it common. Sometimes asking price is not what is agreed to in pm and text conversations. There are a number of things that can go wrong with that. Sometimes someone takes an intentional loss because they want to move something quickly because they have a deal on some unobtainium they have been hunting for years that the sacrifice is worth it.
Some people like your idea and i have seen it used elsewhere, even there price goes poof on my deals when deal is done. Those worthpoint places skew the real market by taking ridiculous high auction prices from 2 guys who dropped ridiculous high last minute bids at close of auction to think they would get the other to back off. Thats how a data plate off a WW1 1917 Browning sold for $1,500. And I have seen far worse where the auction closes at 90,000 for something and it is relisted in 5 days because it was a $3,000 piece and they blew it up and walked away messing up a legit auction so they could try to PM the seller after auction closed from a different account to see if they could scoop it.
I realize these particular examples are not what your asking but attempting to illustrate why current research is best.