Why you're recommend it?
I said I don't recommend it. Even using the outdated guide's method it can still result in you being scammed because most likely the person you're trading will want you to go first, resulting in either you trading your stuff away and him disappearing/you paying his coins and him not trading you the stuff you wanted and again, disappearing.
Flat coin trading is honestly just generally not recommended. If you want something from the coin shop, just try to trade for that item specifically if it's tradable.
Thanks