We have both paid ads and free ads. Put the most important information at the start of the ad. Use standard abbreviations. Know the value of what you are selling. Too high, and they won't buy it.
People perceive that as a come-on.
Don't advertise one item and then sell another. This is illegal, and it could get you hurt. In the ad, include the information that you as a buyer would want. Don't say something is in mint condition unless it looks like it just came out of the factory. The kinds of buyers you would attract with such deceit are probably not the kind of people you want to associate with.