Any service that takes any kind of funding from businesses has an obvious conflict of interest (see BBB, Yelp).

Any service that relies on consumers for funding will have limited resources and thus limited scope (see Consumer Reports).

And of course rating businesses on things like customer service and response to complaints is inherently subjective.

For small stuff, you're best off with a quick Google for any major problems, and then just trying for yourself. For big stuff... well, lots more Google.

Checking reviews on Reseller Ratings used to be a decent bet for online shopping, but they seem to have gotten awfully far in bed with the resellers. These days I do virtually all online shopping on Amazon, anyway.