I think that what is even more important is that when you do sell something and something goes wrong or the client isn't satisfied you need to respond immediately even if there isn't anything wrong with it and it is a glitch that is happening on their end.
Response time on your account is really important and one of my biggest mistakes I made was not to check frequently enough, (Also because I wasn't selling for a really long time) so the day I actually did sell I replied too late, (Possibly even a couple days after) and that really affects your later sales and reputation...