Complex sentence: Convinced he is washed up, Joey sells his "Baby" (his beloved trumpet) to Nate, a pawnbroker, for $8.50; but when Nate puts it in the window, it has a $25.00 tag on it.
Split into simpler sentences: Convinced he is washed up, Joey sells his "Baby" (his beloved trumpet) to Nate, a pawnbroker, for $8.50. Nate then puts it in the window for sale with a $25.00 tag on it.