While I don't have a "proper" AV setup. It still fufills my needs, and every piece of hardware I bought I've research throughly. So mostly my own opinion of it, and a little bit of professional reviews and forum opinion.
Difficult subject this. My purchasing decisions come down to a whole range of things. First and foremost detailed analysis of the specifications - there is no point buying a bit of kit unless you know it is capable of doing what you want. This is normally supported by reading reviews (magazine and internet) and hearing feedback/comments on the forums. And for expensive/critical kit there is then the auditioning phase (ideally including home trial). Finally, and I know this really shouldn't matter, the looks of the thing do have some bearing.
All in all I don't think you can rely on a single source to make your decision. I tend to find magazine reviews are a little too shallow and, especially for things like Blu-ray players, tend to be overtaken by events very easily (e.g. 'lows' rectified by firmware updates). Forums are much better as multiple opinions means advice is error checked/argued by others but even then factions form and 'favourites' can emerge - the Oppo 'mafia' for example - and then everything else is shotdown and withers before such postings. And as for dealers - some are great and very knowledgeable - others are the complete opposite.
A little forum advice can be helpful but i really always audition things before i buy them. Sometimes this ain't possible but i defo recommend it .Forum advice just like mag reviews are only somebodys opinion ,yours may or may not match.