I guess that is part of my issue with GM Spence. If I was a manufacturer I would want to have at least some control over the distribution/sales/service network when it comes to issues that may reflect badly on the manufacturer and frankly vice versa. I suspect they do. The buying public, in my opinion, does not see that separation when buying. They go to the Chev or GMC dealer, they may have or not a favourite dealer.
Over the years I have watched and read with interest how the dealer network(s), following your logic, has screwed customers around who have been dead nuts loyal to the Manufacturer, not necessarily the dealer, over the years. Someone in those horror story threads inevitably says call Mary Barra, like she would give a crap. Something new comes along, like the C8, and the "scams" start again (just like the C7 Z06). I was like that with brand loyalty for a long time. No longer.
Just bought a new F150, ordered it and the sales manager asked me for not one cent. Said he would call me when the truck came in and we can sign the documents. His verbally quoted price and vehicle description was exactly what was on the sales contract. That is the kind of person I want to deal with. There are horror stories about some GM dealerships and what they do to customers, they do not in my opinion deserve the loyalty they get. I see the two parties firmly lumped together. You might bitch about the dealer but anyone listening hears Chevrolet.
Admittedly not all dealerships operate in the manner of asking for $70K in deposits but obviously some do. I strikes me in this particular case based on what the OP has stated that the dealership was not going to give him his money back, if he could not come up with another plan he was buying that car. I also believe that there is no guarantee that the dealer will even get three allocations. Then what?
Just MO.