As someone who got his start in SaaS (though we didn't call it that then) offering this exact service, Amazon is going to be very annoyed with you once they're

As someone who got his start in SaaS (though we didn't call it that then) offering this exact service, Amazon is going to be very annoyed with you once they're handling DDoS attacks on your behalf. Be selective of your clients and cut loose quickly. There are people who will sign up for your service just to go shit-talk on EFnet, and the wrong person will result in your entire service going down.