It's more important to be warned about bad sessions than to be notified of good ones.
Good reviews are subject to personal preference and may, at times, be self serving to the reviewer. Also, many of us know that a really good review will only come back to haunt the reviewer in terms of causing rates to increase or appointments to become more scarce.
Bad reviews allow us to save time and money.
I don't mind hunting for hidden gems. It takes time and costs money to find them. When I do, they're my secret. This is my payback, just like a drug company having patents. I'll be happy to share bad reviews as a public service.
Just my opinion.