It is a simple mission, just sell "non-dairy products" to 50 customers and the mission is completed. The safest place to do this is on the bridges, because there's less police presence. Any bridge works, but the long and thin one between Little Haiti and Leaf Links works best. However, be aware for Patrol Invest Group, the security guards in blue. They will shoot at your vehicle, and attempt to pull you out of it. Cops will do the same. When you get a wanted star, stop selling until you lose it, or you'll have the cops after you for the rest of the mission. Once you've sold 50 products, exit the vehicle or stop the mission to finish.
HINT: It is very easy to do this mission by the Pay'n'Spray down in the southeast corner of Vice City. You can park next to the PnS, sell until you get three stars, and pop right in to wipe your wanted level.
An alternative is to head south to the docks where there is plenty of foot traffic and a Pay'n'Spray.
In some cases, users have reported that their car horn does not work. Resetting your video settings to default levels may correct this error. You may also try tapping the horn key once for a very short duration, as holding it for longer than a quarter second might not toggle the jingle.
The Cherry Poppers ice cream factory will now generate $3,000 / day.