Different people are experiencing different things, it seems, although I think the majority of it is what people are expecting. Some want crystal clear sound as if you were playing a CD. I can tell you that if that is what you expect you're barking up the wrong tree, a transmitter no matter what brand is not going to give it to you.
I personally love the iTrip, it has increased my usage of my iPod. Sound quality is good, sometimes after a rain a station is broadcasting a stronger signal and I get interference from a preset station which I usually did not, or when traveling I'll have to switch to another station when I get closer to a source station transmitting on or near the station I have the iTrip set to. Or there is just drift on the station that day. My point is there will always be a few things that may effect the sound quality of your music, but I should also point out that I also get clear sound in the same location and station were I previously had static. There is just a lot going on. The iTrip has it's strength in the fact that you can select from 100 station and it is digital which means it won't drift off the station you set it to like an analog solution. You also discover tricks to get better sound out of it, so be ready to experiment some with stations and volume settings. I would try setting 3 or 4 presets on my radio and if one is bad at a particular time of day just change it. Good luck. Oh, and maybe you should try different retailer.