I think its kinda lame thats hes sending you pics getting all smug about it. You could have done the same thing and got his hair yellow but proper hairdressers wont carry out a service if it will put hair in bad condition too. Hes got nothing to be smug about just lucky his hair is short and that when he realises its a bubblegum mess he can cut it off easily. Tbh i would refuse service if hes so blatantly undermining your capability and trying to show you up like that.
On the subject of silver, i use affinage and 9.117 is an amazing silver really nice colour and you dont have to worry about leaving it on too long. It has to go on 45 min because it is a deposit only colour but with 3% on correctly bleached hair its not going to cause more damage than any other toner, and it lasts longer than any other toner i have used.