Walk all round the car, slowly checking from top to bottom for any imperfections. Check the Wheel rims for any marks/scratches. Check how many miles are on the clock (mine had just over 4).
Try and get some freebies,... good ones to try are...
Tank of petrol
iPod 'Y' lead (although I've never used mine as I connected a hard disc instead)
Mobile phone charging cradle (depending on your phone).
BMW USB Memory sticks - probably too small for your music collection, but useful for the kids and their homework.
Some BMW cuddly toys (if your kids are younger).
Take your time and enjoy their hospitality,... I think I was at the dealers nearly 3hours before I finally drove off!
It's arrived, e93 M3 Convertible: M-DCT, JzB / extended BB, and most of the options.