I need some expertise with people who do sales

Convince people the product/services you sell is the stuff they need, understand their necessities (active listening) and economic range if possible, offer alternative products, understand your products and prove them, how it tastes/ how you feel, what is the interesting facts about it, ask for extra pieces and review it as consumer yourself, is your product/service that good/bad?

Don't talk trash about competitors, instead say the lack of benefits they have. Study about color theory, and customer behaviour and data.

The 2nd part (how to get people to rate their interaction with you positively although they dislike the company) is tricky but hopefully the majority of people will understand that you in your job in customer support are not identical with the company itself and while the company itself might be badly run you're trying to help them.

About selling itself I would say to avoid being pushy but instead trying to help your customer figure out what exactly they want. Often customers are poorly informed so you should give them a basic idea of what their options are without going into too much detail that would overwhelm them. For example if you own a similar product it's often helpful to explain why you chose that particular product and why it suits your needs best. That product won't necessarily be the right product for your customer but if you're giving them a little insight about your own life (even if it's just an insignificant detail like why you chose that particular __) you create some small personal connection and establish a base of trust.

Know all the small details of the goods you're selling, be the expert in it. Even you are new to this field, you could learn day by day. Emphatyse! Empathy is what really makes people feel, that you are not just a random salesman. This surely will help you to improve the reviews. Even if they didn't like the product after all, they will remember a nice person who assisted them. This may indeed change review score points "1up". Not 2 but 3, for example: way better! Good luck!