With this command, you will be able to trade with him whenever you want, he can't, move, die, or despawn! He also has new trades such as.....
1 Emerald = 5 Diamonds
6 Logs+ Raw Porkchop = 10 Charcoal
5 Diamonds = 9 Barriers {May glitch around but actually works, please excuse this minor flaw if it doesn't work right for you, Thanks.}
And much much more! (Please note that he will spawn behind your command block. Thank you for undeerstanding. ;)