“On Trust” & “Paid For” for are one of the oldest dog tricks that afford as much entertainment as anything a dog can do since the early 1900s. It is not the easiest trick to be taught but can be elaborated on and presented in several different forms to impress most people.
To teach this trick call your dog to you, allowing him to stand up or sit down, as he desires, and hold his head steady with on hand, while you balance a piece of treat on his nose.
Say to him, “On trust, on trust,” steadying and restraining his head from moving with one hand and holding up a threatening finger with the other and repeating the words, “On trust, on trust”.
After which, release his head, saying “paid for,” and give him a little chuck under the chin, that will cause him to toss the treat up and catch it. Of course, in his earlier attempts he will not be able to catch the treat, but he should be allowed to eat the treat after it land on the floor.
Continuous repetition of this training will produce efficiency. Over time you should stop restraining his head with your hand and allow him to balance the treat on his nose until you give him the words “Paid for.”
He can also be taught also to hold the treat between his teeth and not to swallow it until told to do so. This trick can be made more impressive by holding a conversation with your dog. For instance, you might say: “Buddy, old man, here is a very yummy piece of treat, but it is ‘on trust.’”
Slightly emphasize the word “trust” and then go on and say: “I am glad you dislike to eat things on trust, but this I have just learned has been ‘paid for,’” emphasizing the words “paid for.”
Your dog can also be taught to toss the treat on hearing a certain number. To teach this, balance it on his nose and hold his head while you count plainly and deliberately, one, two, three, and then chuck him under the chin. Until he has had a great deal of practice he will toss it up as promptly at one, two, four, as he will at one, two, three, but he must be drilled until he will not toss it until he hears “three,” and it will make it easier for him if you slightly emphasize the “THREE” word.
In time you can use many combinations of figures and he will wait until he hears the emphasized “three.” In working him do not make him wait too long before you say “three,” and allow him to eat the treat.
“Trust” and “Paid For” dog tricks are considerably difficult to master and requires plenty of patience from you. Remember, do not punish your dog if he can’t master the trick, and rather blame yourself for being a lousy teacher. 
In any case, enjoy training and have lots of fun along the way.
