Sure, you do. If I take money from Colt and then write about Colt or shoot their 1911 for a year and blog about it, you honestly think the money played no factor in what I wrote? Or even played a factor in what gun I chose to feature in a year-long series? Does anyone think Colt pays people to write negative stories about their guns?
Once you start accepting money to write about a product, your writing is immediately suspect and can't be taken seriously.
If you want to make it even worse, don't disclose from whom you've received compensation. Take Caleb's blog, for example. As best I can tell, he takes money to write about certain companies and products. However, he and his employees may also write about products without any support from the manufacturer. But I wouldn't know because he doesn't appear to be upfront about who has paid him money and who hasn't. (Maybe there's some fine print on his blog where he discloses this, but I haven't seen it.) Therefore I just dismiss whatever he says, since I can't know where his bias lays.
It's pretty simple.