I share my apartment on Airbnb. Counter review is not a thing since (as you said) it’s not possible to see the customer’s review until you post your own (or after the 7-day review window expires, at which point you can’t review the guest anymore). I’d also add that there is not an easy way to know how a guest reviews the hosts. The guest info you see only includes past host reviews. I’m sure it’s possible, but Airbnb does make it very difficult.

I encourage anyone to post real honest, negative reviews if the experience is indeed bad. Airbnb seems to do a good job building the system, and I feel guests are protected quite well, from a host’s perspective. Honest reviews help good hosts, and I would think I’m one of them :)