if they suspect anything they can find out.... trace your ip addy.... and you would be surprised at the dumb $hit i catch people doing.... it dont take much to put 2&2 together...
Fish shipments frequently get opened for inspection as well, especially in states with many illegal species.... I suspect this is how many people are caught.
Check the buy/sell section and you'll find an article about a guy caught selling fish to illegal states. Hefty fine, 3 years probabtion, banned from commercial dealings in fish, etc. Smart companies won't sell to illegal states. It's not worth the risk.