If your client has bad review, maybe the work that has to be done is on his side, not yours…
Had the same issue with old client , he was arguing “Ben, I get so much bad review all the time, blablabla, people are crazy, fuck them off, I want to buy fake review to hide bad ones…”… After a moment of discussion with him, to understand what was behind these complaints, it appeared that it was his fault, that these products were poorly finished and therefore deteriorated quickly (they were wall stickers), so people felt robbed and they expressed their discontent.
Talk to your customer, try to find out more about their sales process etc… you have to dig into the negative reviews, what they say, if they say anything at all, because if it’s just putting 1 star it’s worth nothing.