I too don't like those who refuse to leave feedback until they have received feedback. I will always avoid dealing with these people where I have the choice (for example two people offering the same item). If I am also somewhat leery about dealing with somebody for some other reason, I always check what their feedback pattern is like. If they have a habit of leaving feedback immediately after receipt of payment, I will always give them the benefit of the doubt.

As far as shipping costs go, I don't believe that 10% extra above and beyond net postal costs on small items is wrong. This notwithstanding that it is now possible for almost anybody to ship items directly from their home without ever needing to go to the post office. I pay my USPS postage online and arrange for pick-up for free. USPS even supply the boxes that I ship in for free.