^^Yeah, with wet/boat/dip/PCP you will know before you smoke it if you have any prior experience with regular weed.
Though the crystallized/powdered form (angel dust) I'm not familiar with at all, but I would assume it's fairly easy to tell when you've got a foreign powder spread throughout your nugs.
When it comes to wet PCP, though, it's amazingly difficult not to think something's up with your bud before you smoke it (or even buy it).
[edit: oh, and to keep this on topic, when I first started smoking I consistently copped from one guy. From what I heard at school, he had the best bud around and the fattest bags. I felt okay with this because every bag I got from him had buds sticky enough to stick to my finger with barely any pressure applied. After coppin' from him for a few months, he invited me to a party at his house. I went, and midway through a huge fight broke out because a few people looking to grab something stumbled into a room where he was putting wood glue into his bags. Come to find out, he had always been doing that and it was the reason why his bud was so damn sticky.
After that, I was always super cautious with learning to trust my supplier and pretty ridiculous about finding a connect that grew his own product. To my knowledge, though, I haven't come across any adulterated bud since then]