Not listing/posting a price is most certainly a marketing strategy and effective in 50% of instances depending on market target and item for sale.
High end high price items are targeted to folks who are not overly concerned about how much it is but mostly about WHAT it is, cost being secondary.
Getting into swap meets and the like, I also will keep on cruzin if there's no price tag. I'm usually truckin' along to see what's in every booth so don't have time to wait for the vender to stop BSing with some one in order to ask "how much?" I got things to see and parts to look for, and if he don't want my money bad enough, someone else will. With that in mind I ALWAYS price mark my stuff and some with an 'price negotiable' addendum.