A 200-1000ms wait after saying "trade" is a bit short. I think you'll find that a lot of people will fail to trade when the wait time falls on the lower end of that range. Personally I use 1200ms + Self.Ping() as a minimum, but when you're selling stuff it's actually possible to use the sale count to accurately determine whether the trade window is open yet (the sale count will always be 0 if the trade window isn't open).
Also, there is no need to use Walker.Stop/Walker.Start at labels, the bot walker automatically stops while it is executing code at labels.