Well of course if you survey the top sellers then they are going to be
optimistic. They are the ones who are already doing well. Therefore the
result is exactly what you would expect. How about surveying those
thousands (possibly millions) of sellers...
You just need to use the calculated postage option instead of the flat
rate option & you can increase the amount to whatever you need to
include costs & handling. Under that option you are not restricted to
$8.30 (or whatever it is).