I will admit to do $1 ads on Craigslist.
There are at least two reasons I can think of right now:
1- I am listing several pins for sale and I have the choice of putting in the price for one of the pins but not the others and also get accused of a bait and switch or just put in a dollar and assume that a buyer knows that will "several pinballs machines for sale" as the subject of the listing they will need to open up the link to find out the prices. Could I put up a few ads, yes. But I often sell several pins to one person, I am in the middle of nowhere and it often helps a buyer to commit if they are able to get more than one pin if they are making the drive to me. Also if I say "look for my other pinball machines for sale" people never seem to find my other ads or they just don't read the ad that well to realize that I have a few pins for sale. They just look for a price and the photos at the bottom.
2- I am open to trades and offers. No way to put this into the price box, only numbers. I don't want to scare off a potential buyer by a high price. I am very flexible, this is a hobby and I am often open to many possible trades/offers. You can't fit all of that into the subject/title bar, so I put in $1 in the price and figure if anyone is interested in the subject line they will hopefully open up the full ad where I can explain all of the possible things I am interested in to make a sale work for both of us.
These may not be great reasons, but they have worked for me. Perhaps some other method would work better for me, I don't know. But not all $1 pinball ads are scammers, bait and switch, or people with stupid high prices that are hoping to you to open their ads.