A verified user has taken the effort to get his verification completed by OLX. This means he or she is a serious seller.
Also since they have shared their personal information with us, they can be targeted by police and other authorities if they are found to be selling wrong product or doing any other fraud on the platform. This means the user is assuring you that he or she is a genuine seller and is selling a quality product.
In short, verified users are serious sellers who are selling genuine product. You should feel safe in transacting with them. And in case anything goes wrong, you will be able to take action using the personal details that can be shared with authorities.