Learning?

The other day, Amelia asked me to draw some artwork with her.  She came up with the idea that we would draw things and Meggan and Everett could come to our art store and buy them.  She sold a drawing of hers to her mom for $1 and a drawing of mine to her brother for $1 (a dollar I had to give him).  Everett, liking this concept, decided to set up a toy store where he would sell his toys (which happened to be any random household object).  I ended up negotiating the purchase of a flashlight for the hefty price of 5 quarters.  So, all told, I essentially paid $1 for a drawing I drew and $1.25 for my own flashlight.   At what point have you switched from deciding to teach your kids about hard work and the value of a dollar to your kids teaching you that they are indeed con artists?