Absolutely no deleting posts--here's why (and it has nothing to do with teaching people a lesson):

If someone posts a question, and they get input from a dozen other people, answering their question, that's a good, valuable thread for newcomers to read. If they go back and delete their post, saying that the thread is now closed because the question was answered...a lot of that goes to waste. You may think people would not be this dumb, but I have seen it happen.

The same is true of unlimited editing. I've seen people go back, delete their question, and replace it with a 'thank you, close the thread now' note. So, preventing people from deleting their posts or editing them past a certain date is one way to control the stupid and keep things a good resource for everyone. A bunch of answers out of context is annoying, and not useful.

Now, I do have one suggestion--I do think that ads should have unlimited editing options. Editing doesn't 'bump' an ad, so it shouldn't count toward the number of ads a person is allowed to post, even if it changes completely. Editing will allow sold animals to be removed from the ad (which, at present, isn't possible).