How to check if a website is trusted or not?

Could you please elaborate on the steps one should take to verify the trustworthiness of a website? Is it sufficient to merely check for an SSL certificate, or are there additional measures that should be undertaken? Additionally, how can one ascertain if the website's reviews and testimonials are genuine, and not fabricated to deceive potential customers? Lastly, what are some red flags that should immediately raise concerns about a website's credibility?