Originally Posted by vkartikv
Since you've covered most of the important points, let me just add that always be courteous when you communicate with someone. This is the internet and yes, emails are meant to be informal, but sending someone a message like this 'I'll take it for 50', without a signature or a hello, especially when the item has been listed for a much higher price is an instant turn-off.
I think this is a little bit of a misconception when it comes to e-mails. Yes, e-mail is an easy, and accessible method of communication, but it doesn't mean it has to be informal, especially
when it's with someone you don't know (too well). My rule of thumb is: If you're conducting business, show that you can take your business seriously. It's that simple.