I no longer by anything but solo albums approved by the artist, or stuff from a record label that has a good reputation (ie Done Deal / Deal Done Ent., Million Dollar Dream, etc).
Mixtapes = waste of money. Recycled beats, recycled songs, guys yelling over tracks, bad quality.
Collabos = waste of money. Thrown together too quickly, mediocre beats, mediocre effort, easy shot at a quick buck rather than quality music. Occasionally you hear a good collabo, but as a consumer you are only buying X number of CDs, why take the risk on a collabo if you can get a sure thing with a solo album from a good artist?
Albums not approved by artist = waste of money, for obvious reasons.
I do not buy albums even from many of my favorite artists because they are thrown together to make a quick buck. I only spend $$$ on release I feel has been put together with effort and time to perfect the sound. Like Gas says good packaging helps. Make it look like its worth the time.
I think the problem with Hip Hop is rappers feel entitled to sales rather than putting in good effort. Chances are the download aint killin your game its that you dropped 3 albums in a year and they're all 2/5.