Yes, it’s possible to earn ROI through SEO. And it depends on the type of industry your business comes in ROI is earned by increasing the value of your business. With SEO, your brand value increases when your site comes up as the top recommendation when your customers are searching for you.
Let’s take at an example. 320 people search for the exact phrase “veg restaurants nearby” every month (not to mention those who search for slight variants, like “Veg food restaurants near me”).
Being the first result on Google would bring ~110 people to your website every month who were actively searching for Veg restaurants, many of whom had never heard of your restaurant before. Assuming 5% of those people book a table JUST ONCE, this one search term would bring you more new customers every year!
So, you just need to make sure that your SEO strategy is strong enough to popularize your brand people. Only then you’ll be able to earn some ROI through SEO.