1. A method comprising: receiving a request, from a user, to perform an action at an online marketplace, the action including at least one of buying, selling, and posting at the online marketplace; retrieving a plurality of risk assessment factors associated with the action, the risk assessment factors including at least one of a phone number of the user, a locale of the user, value of an item associated with the action, category of an item associated with the action, the action type, a description of the item a listing site, and an Internet Protocol address of the user; performing, using a hardware processor, a risk assessment process by feeding the risk assessment factors to a supervised learning algorithm, the risk assessment process identifying a risk mitigation process; requesting that the user perform the risk mitigation process identified by the risk assessment process; allowing the user to perform the action in response to the user completing the identified risk mitigation process; and modifying the risk assessment process by adjusting one or more internal weights used by the supervised learning algorithm and based upon a result of a post-action analysis of the action.