Consumer Psychology: Free Shipping

I am a sucker for free shipping. Amazon is really great about using this as marketing leverage. I buy some kind of expensive hardcover game rulebooks on a regular basis. I've started using Amazon rather than my local hobby shop because it's 30% cheaper on anything I want to buy. If I'm willing to wait that is.

The most recent thing to come out is 30 bucks. Amazon will sell it to me for $18. However when it's only $18 I have to pay $4 for shipping since it no longer qualifies for free shipping. I'd still be saving eight dollars, but of course now I'm trying to think if there's anything else I'd want to have... Obviously it's very ingenious.

Newegg did a similar jedi mind trick with my $300 video card-- it was free shipping for a limited time if you order TODAY. Now I was in impulse buy mode already, so it didn't take much convincing.

Compare that with the insane policies of my favorite popcorn company, Yoder popcorn. Yoder is great stuff but the minimum shipping for any amount of popcorn is $10!!! Often times shipping equals out to be twice the cost of the product itself. I probably wouldn't mind paying more for the individual bags if shipping was 5$, or free after a certain amount.

I'm sure there's a social psychology principle behind all of this, but it's been a few years since college etc.