When a state revenue agency discovers your customer’s untaxed purchase, it will bill the customer for the use tax, penalty, and interest. Use tax is also due when the purchaser pays sales tax, but the item is brought into a state with a higher rate. For example, if you charge sales tax at Florida’s rate, but the customer lives in a state with a higher rate, that state can bill your customer for the difference.
When your customer receives a bill, a dispute could arise over whose responsibility it is to collect the tax. Even though you may not be technically liable, you provide a service to your customers when you voluntarily register and collect tax. They do not have to worry about paying tax to the other state.
To read more! Why should I register to collect sales tax for another state? Source: InfoTaxSquare Business Documents Filing In All Fifty States!