Im not sure I understand what you are saying? Why would the $7500 not mean something, regardless of cash or credit?
The way I see it, if I order a new Tesla for say $100,000, and I am getting $7500 back, that takes the price down to $92,250. If a CPO is at $72,000, that makes the difference about $20k instead of $27,750, no?
I am not saying $20k is not a lot, it is, but your also getting a 2 year old car that is older technology. IMO, its not so straight forward.