You could make an anonymous call to the police station and notify them of the dealer. This is a good option since you do not want to be involved in the whole process and your identity will not be known too.
My dad had that prob. Foot traffic upstairs 24/7 plus loud music and voices. Police finally did a raid and there was peace and quiet. U need to let the police know whats going on so they can take action. It might take a while tho
See if you have a crime stoppers program in your area. You can report a crime without telling who you are. The assign you a #. The program has no idea who you are. If your info leads to an arrest you may be able to get a cash award for your info with out having to testify are reveal who you are. You would get a bigger $ for your info if you do identify yourself and testify. Just an idea!
use a camcorder in a car far away. video record the transaction from a distance. make several copies and act accordingly. try to get the media involvemet and support on why the police is doing too little about it.