Totally agree that you should try FABO first. Pretty much a waste of time to have a garage sale. First of all, most people will be clueless as to what you have, and secondly, people want bargain basement prices at garage sales. Here are a few of my thoughts:
1. Ask reasonable prices. You don't need to give stuff away, but asking ridiculous prices is counter productive.
2. Take GOOD pictures. Good pictures will save you answering a lot of questions.
3. Make the Title line in each For Sale ad descriptive enough that people can tell what you are selling. It drives me nuts when the title is just something like "Window Trim". What car, what year, and which window???
4. Give an honest description. If the parts have flaws, scratches, broken tabs, pitting, etc, mention it.
5. Get some USPS Priority mail boxes (one of each size) and see which box each part will go in. That way you can advertise the shipping cost with the part, or list the parts with shipping included and just bump up the price to cover it.