I can answer that in 2 ways - pre purchase and post purchase - so I'll do the easy one first.
Turn up in a Ferrari - they'll let you do what you like!!! This is something I intend to make use of (to get some test drives!!) this summer!!
I wondered about this when I first started looking - whether they'd just ignore me, or even worse chuck me out!! I'd make sure I was looking tidy, make sure I'd had a shave etc etc. I just didn't know what to expect.
But to be honest, the vast majority don't care. I'd always make sure I let them know exactly what I was looking for, before I started wandering around, and to be honest every single one was fine. One of the dealers did tell me that I'd be ignored in a particular dealer, if I turned up dressed as I was - so I fully intend to go there in the Ferrari this summer dressed as scruffily as I can!!!
Of course most of the dealer showrooms are quite quiet compared with a mainstream brand, so it's hard to be ignored, but I got a far better reception and level of service than I would expect (through experience) in a BMW/Mercedes dealer. They can be really pompous - which I find absolutely hilarious. Of course, if I turned up at a BMW dealer in the Ferrari - they'd probably lay out a red carpet!!!