Frank sells Sue a horse for $60. Then he decides he wants it back, but Sue makes him pay $70 for it. Then Sue changes her mind and buys it back from Frank, but for $80 (Frank is no dummy). Finally, Frank buys it back from Sue for—you guessed it—$90 (Sue is no dummy, either). At this point, who comes out ahead?

Follow the money; H means that person has the horse.

Frank | Sue | |

+60 | -60 H | |

-70 H | +70 | |

+80 | -80 H | |

-90 H | +90 | |

Totals: | -20 H | +20 |

So Sue comes out $20 ahead. Frank has his horse back, but he paid $20 to get it.