You ever see a dump truck that says “not responsible for broken windshields”? Guess what. EVERY truck — this is US law anyway — is responsible for securing its load. So why do they have the sticker? So you don’t bug them about it. Or at least so most people don’t bug them about it. They also say stay back 200 feet. That’s not a law. It’s just a bumper sticker and is equally as enforceable. If they crack your windshield because they didn’t secure your load, you (or rather your insurance company) can go after them. But the truth is, most insurance companies just write off so many broken windshields per however long anyway, they won’t go after the company even if you have proof. But they could — and so could you.

Post the review anyway. Or at the very least post a review that says “the terms say I can’t post a negative review so believe me when I say the service was acceptable.” It’s not a negative review. It’s not a positive review either. It’s a neutral review and it calls out the clause. It is heavily implied to be opposite of what you said. You said the work was acceptable, implying it’s unacceptable. If you used the same tactic and said the work was great, the opposite would appear true, that it was not great. But acceptable is not great. So say it was acceptable and imply you were forced to say that. Thusly, an intelligent person will see your message for what it is.