If you buy something with your own money you've got a different bias to counter, confirmation bias. That is, "I've paid good money for this so I'd better prove to myself I didn't make a mistake".
I used to work as a full-time review journalist, as Labs Manager for PC Magazine and Tech Editor for PC Pro with later occasional freelance work for other titles. Both magazines that pioneered, in the UK, using objective test data as the core of reviews (hence "Labs Manager"). The norm there was to borrow products for review from the manufacturers and return them after review. Although this removes the "getting it to keep for free" bias and the "I bought it so it must be good" bias it doesn't eliminate bias altogether. For one, you've got PR companies associated with the manufacturers who can affect you in a number of ways from pestering you, threatening you, offering trips to "see the manufacturing plant" (booze-ups in sunny places), right down to simply knowing journalists innate biases and steering product towards or away from individual journos. Both my former homes were excellent at ensuring pressure from the advertising side of the magazine didn't affect editorial but that isn't necessarily the standard everywhere so that adds an additional possible bias.
The only sure fire way to eliminate all but some residual personal biases is to: 1) Buy the products to be reviewed anonymously, 2) Dispose of the products after review, 3) use objective measurable data as the core of reviews, 4) have objective, stated, criteria for what's 'best'. The problem is that this costs a *lot* of money and people just aren't prepared to pay for the end product nowadays.