Selling via Realtor = Higher House Price?

Are people who are selling their homes justified in threatening the general public with an increased asking price for their house when they are forced into listing with a realtor?

I don't get it.

Today on Craigslist, the owners of a home in Royal Oak threatened us all that this was the last chance for us to buy their house privately, in their words "LAST CHANCE - We will be listing with a realtor next week and the price will be going up!"

I saw this same scenario play out earlier this year. A private house sale in Atkins was listed on Craigslist and UsedVictoria. They started at one price, lowered it after a while, then threatened that they were going to get a realtor. It didn't sell, they then listed with a realtor for their latter asking price. It still didn't sell, they lowered the price. It did finally sell, I believe for less than any of their asking prices.

What makes a home seller think that if their house does not sell privately for a certain price, that it will sell for a higher price when listed with a realtor? What makes the seller think that I may not be willing to buy their house at today's price, but I will buy it tomorrow at the realtor's higher price? Who these days, when buying a house, is not looking at Craigslist, UsedVictoria, and the TC on their own time?