As UW said, lots of people including myself track IPs and that's your biggest danger. Different scripts do it differently, and some of us just rely on the ol' noggin and do pretty well with it
The multisubmitters I blacklist are the ones using different emails from the same IP.
I wouldn't sub to anyone without prior approval in any case. Getting that sort of approval from all the big LLs, who you obviously want to submit to in order to give value to your customers, will be a big pain in the ass to say the least. Upon further consideration, I'm going to suggest with several others and say build them, but don't submit them yourself