<human>: So I have just been dealing with a second hand instrument dealer, I have now sent him my old saxophone to trade for a different one of his. I sent him pictures of just about everything, serial number, where it was made, the condition of each part. It was then agreed I would send it, and when it arrived in one piece I would transfer the gap (as the new instrument worth more) and he would then send me the new instrument. The instrument arrived (posted, as this is Australia, a rather large place), in one piece, and he decides he doesn't want it. He says I have to give him $40 for him to send my saxophone back, this can't be legal? Can someone point me to some legislation or law that says I shouldn't have to pay him anything?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: I sent an instrument to a store for a trade, they changed their mind, I now have to pay to get my saxophone back.