Freebase Dali

Yea I've been there. I assume you're talking about buying herb, in which case you'll be treated legit like anyone else who buys from coffee shops. When I was there they still sold shrooms at the smart shops, although I seem to remember something about them doing away with that a while back. Maybe s_k can confirm.
Regarding anything else, you're very likely to come across shady dudes walking in the street and when they pass you they mutter "ecstacy, cocaine?". Don't even look at them. Fortunately before I went, I had done some research and the general consensus on those guys were that they were pedaling fake crap to clueless tourists, which is apparently an extremely successful market considering how many times I was approached.
Heh, eventually my friends and I got so sick of those guys accosting us that when we saw one coming to us, we started asking "kittens, puppies?"
They'd look at us weird and go "ecstasy, cocaine?" and we'd say something like "nah, we have plenty, but we have kittens and puppies we're trying to sell, you want some??"
The guys would just walk away at that point and we started doing that for the rest of the weekend, laughing our balls clean off every time at the reactions we'd get from these guys.