While one may not be able to complete the entire business buying process online (with the exception of sectors like - internet businesses etc..), meeting the seller before buying a business is generally required to understand what you are getting into.
However, the initial search and discovery process should be restricted to online only since it is found to be the most effective method. Within a matter of few minutes, a buyer could narrow down businesses that he / she thinks matches his requirements. Post this, the buyer can rech out and connect with business owners to take it forward. Here's a list of businesses for sale for you to get started: https://www.smergers.com/businesses/businesses-for-sale-and-investment-opportunities/s0/c0/t0/