every other 2nd hand car dealer is a crook....probably you already weighed your options and know there is no recourse.....so you launch your online campaign against them to justify your loss.....if you do not wish to go to extreme of burning down their shop....may i suggest cheaper relatively risk free and more cowardly ways to appease your anger. these will not get your money back but at least might pacify you emotionally.
1) post their phone numbers online offering sexual services
2) hang around the shop and scratch their cars or puncture the tires
3) splash paint on the shop, superglue their locks, cut their phoneline/elect, do damage to the shop
4) track down the personal info of the persons invovled and smear them/ their family