Global Communication, Boards Of Canada, Delerium, Synaesthesia, Intermix, Moe., String Cheese Incident and more.
Touch wood, I haven't bought a clinker yet this way. This is all pretty obvious stuff, but part of the trick is to cross-reference the references against other people's purchases. It could be that only a few people have bought Album X (which you know you like or you have) and then one of the daft buggers has gone off and bought a Nana Mouskouri CD as well (maybe for their granny or stone deaf cousin).
Always check out "See All Customer Reviews", cos it tends to attract gushers who give everything 5 stars. Pay particular attention to the featured reviewers and look at the range of other stuff they've reviewed to see whether thier overall taste matches yours.
The great thing about this forum is that (for me anyway) you've formed such a useful jumping off/reference point.
And if I have any doubts, all I have to do is imagine a post from Tony Lonorgan saying "just buy more krautrock"...