Yeah, when a woodworking channel spends half a video "testing" some new product on their table saw, I begin to feel like I am being sold a bill of goods.

How to you distinguish that from someone trying out a product to review it?

It's a tough line to walk. For something like woodworking, I suppose I'm not looking for "a new product"?

Perhaps there should be separate channels in such a case: the wood-worker-reviewing-stuff channel and the making-things-from-wood channel.

It's one of those grey areas that comes down to the integrity of the channel owner. There are probably people who never find anything wrong with stuff they're sent to review and there are people who give honest reviews. Conflicts of interest are everywhere but it doesn't mean that a potential conflict of interest automatically translates into bias.