Performs the MyTradeMe method: Retrieve a list of items currently for sale
using the "query" string provided - should be the "MyTradeMe/SellingItems/All.xml" part of the url. It shouldn't include "http://api.trademe.co.nz/v1/".
public Items SellingItems(string query) { if (_myTradeMe == null) { _myTradeMe = new MyTradeMeMethods(_connection); } return _myTradeMe.SellingItems(query); }