Person 01: "Yo, Hwut R you doing?! I need help, here!!
Person 02: "No can do!!! I'm busy, "Melting a Path", from the house to the driveway!!!
Person 01: "FINE, I'LL Get YOUR BRO, to help me!!!(grumpy muttering)
To be humiliated by your opponent in an activity of competitive nature, or to be conned or outsmarted by something/someone.
If one was to beat another at a sport such as pool, and said person beat the other by "8-balling" him, then he could've been said to have been "sold up the garden path" by the victor.
If one was to have bought something for £400 that could normally have been purchased for a fraction of the price, he could also have been said to have been "sold up the garden path".