public string CancelTradeOffer(ulong tradeofferid)
{
const string url = BaseUrl + "CancelTradeOffer/v1/";
var data = new Dictionary<string, string>
{
{"key", _apiKey},
{"tradeofferid", tradeofferid.ToString()},
{"format", "json"}
};
return WebUtility.UrlDecode(_web.Fetch(url, "POST", data).ReadStream());
}