I changed my mind for one time, but I notified the seller by message immediately. I think everybody in this society should be responsible. Not only buyers but also sellers.
I once sent a message to a seller to order her items shortly after she done updating her post, but never got a reply from her and even found my message had never been read. I just saw she posted another public message that announced she got tons of message, and the items were noted "gone" one by one. I just don't know how she handle her message: read updown conveniently? or she did get a lot of interests ahead of me. Certainly, that didn't annoy me. Browsing MMs' pretty DDs and buying something are fun for me. Just LZ's post reminds me this. And I like to pass a message to everybody----be "having rules" and considerate! :-)
(sorry about the annoying English, I am writting this on my working machine)