Its by tender....they will invite public tenders with
specifications such as "3000cc, xxxx length...etc."
then whichever company can offer within spec and lowest price gets
it.
The last car which won the bid for 1-star BG / RADM ranks was the
Audi A4.
The 2 and 3-star chiefs get Mercedes E200. I think the CDF's car is
an armoured version, not E200, but Exxx although its badged as
200.
