There are several factors to consider a business as a high-risk business. Here are the few: You may have too high of a chargeback ratio.
You offer recurring billing, subscriptions, or a free trial. You sell high-ticket items. You may be involved in an industry that has a reputation for having high fraud and chargeback rates.
Remember the fact that ALL merchant accounts carry risk. Banks want to make sure that their time spent on paperwork and disputes is worth the return.