One of the best ways to remove negative review bullets from the gun is to have way more positive reviews. If you have 100 5-star reviews and one troll, searchers can tell the difference. If all you have are trolls, nobody wants to cross that bridge.
Always, always, always ask your customers for a review after any sale or service. And you don’t have to beg.
Finish your transaction with, “thanks for choosing us today. If we earned it, we’d love for you to leave us a quick review on Facebook.”
Customers appreciate that you care about their opinion and want to provide great service.