it's the 'internet mind game' thing.
We are used to looking at prices and stores that give free shipping. When we think about a purchase, we subconsioiusly think about taking that much money out of our wallet, handing it to a guy, and being handed the product.
Hence you see a price, and think of handing over that much cash as being acceptable, and you want to buy.
However, you then initiate contact and reality sets in. You now must match a person's schedule, he wands immediate commitment to buy, you need to meet somewhere, etc etc. Now unlike a store purchase where you see the add and think 'Okay I will buy at that price' and you know you can show up pretty much any time and get it, you now have a limited window to commit, and you have to put some effort in.
That changes the dynamic. A widget at the corner store may be a fair bargan at $100...but if you have to drive across town and be at a store in a very small window, that $100 may be too much when combined with the hassle.
Of course, this is the exact opposite of the syndrome where a guy will spend $10 on gas and 2 hours in the car to get a handgun for $450 vs the $500 pricetag at the local shop.