I'm 4 years sober from heroin now, so I can speak from my experience using in Los Angeles from ~2008-2011.
Balloons are typically sold in .1 gram quantities, with lower quality heroin. I do recall buying balloons wet with saliva, but only some of the time. An acquaintance told me that it used to be standard practice for dealers to use young Mexican children to sell dope by this method on foot in Skid Row, but that the city had really cleaned up downtown. With the popularization of cell phones, the delivery system described in this article became the standard.
Higher quality heroin was usually sold by the half gram. Instead of being in a balloon, it would be wrapped in plastic torn from a grocery bag, tied off or melted to close and seal it. I don't recall these ever being spat out. They would often hide it under the hood in their beat up trucks or minivans.
I never got customer satisfaction surveys from dealers. I'm sure that the dealers had customers or friends from whom they got feedback on their product, but I was never one of them.
A dealer's number was quite a hot commodity. You couldn't just call the dealer up and expect to get served—you had to be introduced. And the dealer would often throw in a free bag if you bought x number of them.
The result of this was that one user would have the dealer's contact information, and would make a buying run for other users who didn't. If they bought enough they could keep the free bag, or otherwise pinch off the bags that they acquired for the other users.