I have always had pretty good luck with selling goats on Craigslist. There are a couple of things that help when writing an ad to post:
1. Be descriptive - I am always leary of an ad that simply says "purebread nanny goat for sale". I kind of get the feeling that maybe the seller isn't very up to date on their goat information. I worry about the quality of animal that comes from an ad with such a lack of description. If the seller didn't have time to write a little bit more about the animal in order to sell it, did they have time at all to care for it? I find it always makes a goat more appealing if the ad has a good description of the animal. Things like age, exact breed, registration, disease status, general health, and any breeding/kidding info are always helpful.
2. Don't be too descriptive - While I like to get a good snapshot of the animal from the information in the ad, I get a little weirded out if the ad is too descriptive. A Craigslist ad is not the place for a thesis on proper goat management. A super long ad makes me feel that perhaps the seller will be very picky about who they are selling to and give you the third degree if you call.
3. Use good pictures - Nothing hurts an ad more than a blurry, dark cellphone picture. If you don't have a good, in focus picture of the animal to post, don't post a picture! Take a good picture with proper lighting of the whole animal. Also be sure to crop it so it only shows the animal for sale. Try to never take a picture in the barn because the barn usually has poor lighting and a dirty barn is a terrible background to use. Take the picture outside during the day with someone holding the animal or at least the animal looking at the camera (no butt shots please!).
4. Tell the truth - Be sure to give a reason why you are selling the animal. It helps to give a small hint of why you are not keeping it.
5. Don't tell the whole truth - You can omit some stuff and save it for after the buyer contacts you. If the goat is a jerk and doesn't like to be milked then maybe it's best to just say in the ad that it "would make a good companion animal".
6. Don't harass the buyers - It's not necessary to put in the ad that it needs to go to a "good home only". That is pretty much implied, duh. Also never say "Be sure to put "blah blah blah" in the subject so I know it isn't spam". You are going to get spam anyways so just freaking get over it!
7. The Price Is Right! - Research what the going price is for a similar animal in your area. Ask around, look at similar ads, keep your ear to the ground. It does no good to ask $400 if the going rate is $100. You aren't going to be able to sell the animal for $400 EVER. Get. Over. It. And lower your price.
8. Don't repost or renew the ad without changing it - I surf Craigslist often so I know when I have seen the same ad 5 weeks in a row. If you haven't had any bites on an ad in 3 weeks, change something and try posting again. Don't repost every day! Also if you animal isn't selling you may need to look closely at the main deciding factor in your ad ---- THE PRICE! Lots of times I see the same ad over and over and think to myself, "Should I email them and let them know that the reason they haven't sold the goat is because they are asking a ridiculous amount for that animal?".
9. Know your audience - Craigslist is a great place to dump an animal quickly and cheaply. It's not the place for a fancy animal that would only be in the price range of very high-end buyers. It's fine to post a high quality (AKA: high price) animal once to see if anyone bites. But don't be shocked if no one goes for it. If you have a really fancy animal for sale then you will need to branch out from Craigslist and go to the place where more expensive buyers will be looking. There's lots of special groups on Facebook and other place on the internet for selling specialty animals.
10. Be picky about your buyers - You don't have to sell your goat to anyone. Create a relationship with the buyer and make sure they are someone you feel comfortable with. Ask them questions and give them lots of information on the animal they are looking to buy. Don't be afraid to turn someone down. They will get over it.