Defining links as good or bad isn’t always the best way to approach it - you would be better to consider whether a link is relevant & adds value to your website, or if it doesn’t. It’s also worth considering whether that link is actually drawing good referral traffic through to your website - as referral sales are another great product of well-targeted Digital PR & are definitely something you should be aiming for if you have an ecommerce business!
Good links are fairly self-explanatory - they are genuine links from trustworthy sources which are relevant to your website. They are acquired naturally through Digital PR & generally offer some level of value to the user, this can be through your expertise or research, which helps to showcase the expertise of your brand - another great trust signal for Google!
By contrast, poor quality backlinks can potentially harm your website - Google penalises link profiles which are heavy in poor quality links - mainly as these tend to be the result of poor SEO practices or dodgy over-optimisation! Regular link auditing will help to ensure that you are keeping your link profile in check & free from any potential penalties.