Dealing with negative comments
Many businesses will at some point have to deal with negativity from followers and customers. Hopefully, if you have a good product and provide great service, then this is not going to happen too often and your bad comments will be short-lived.
There are 'trolls' out there who have nothing better to do with their time than post negative comments. The best thing to do with them is just ignore them, delete their comments and block them. However, there will be real customers who have real concerns and complaints and they may post negative comments publicly; there may also be people who really want to lash out to gain your attention as quickly as possible and spread the news to their friends too!
You need to deal with complaints as quickly as possible and be as transparent and authentic as possible. The best thing to do is apologize and say how sorry you are to hear of the inconvenience they have been caused and offer to continue the conversation and deal with their concern by either private message or telephone. You can then deal with the issue privately, give your customer the full attention they deserve, and decide on your next course of action or compensation.