That's exactly the problem I see with this site and the others out there that try to accomplish the same thing. And really, it's like any review site for anything - someone who is satisfied with what they got isn't that likely to post about it. Somebody who was dissatisfied is VERY likely to post. Especially with something as emotional as a checkride.
As a CFI and active on various forums, I have come to realize that if someone fails a checkride, it is VERY rare that they will feel it was a valid bust and "own" the failure. More often they consider it a completely unreasonable call on the part of the examiner, the examiner is a crook, the examiner is just running a scam to get retest fees and pad their income, etc., etc., etc. I see and hear it all the time.
And with a site like this, there's really no way to proof it. How can you check that a poster actually did a checkride with that examiner? You can't. It's not like Amazon's "verified purchase". So you're left with just accepting whatever people submit, and as stated above, is just ripe for abuse.