This shit isn't real. A car is worth what it's worth. This is how the $4000 push pull or tow sale works:
Dealer marks their cars up more.
ex. 2007 Cobalt sells at auction for 5,000. Dealer lists it for sale for $10,900, a $5900 mark up. So you pay 10,900 - 4000 = 6,900. Lets assume your shitbox is worth $500. So the dealer draws 6900 + 500 = 7,400 for the car they paid 5000 for.
I really hate this shady shit and am sickened every time someone falls for it. Always deal on BOTTOM LINE only.