You have got the wrong idea. Maybe the place you have in mind is The Castle on Third Road. Whips and chains are not part of the service at DD. It is more about you, two girls and a few toys. If that doesn't interest you maybe Boyztown is more your style.
I think you will find the the requirements will vary from company to company. As I posted previously I put down less than 50%. At the time I only had a non-immigratnt type-O visa.
Some of the information in the OP is not strictly correct. It is possible to obtain finance for a new vehicle in Thailand but you might have to shop around. You will need at least a non-immigrant visa and a steady GF to co-sign. Both the car and the finance can be in a farangs name but you will probably need a 20 or 25% deposit.
It is not true that all service stations sell fuel at the same price.