That's a crack up. 'Uhhh...I dunno, they can definately ticket you, but when it happened to us they didn't'. There's nothing like people giving advice when they really don't have a clue.
Check your locality, but there is no federal law requiring compliance with the capacity sticker.
From "ABC's of the California Boating Law"...
Single-hull motorboats less than 20 feet in length which are manufactured
after 1972 must display capacity and safe horsepower information. The
maximum weight in persons, gear and motors is offered as a guide to boaters,
and should not be exceeded. It is not a violation of federal or California state
law to exceed recommended maximums. However, other states may cite an
operator who exceeds capacity and horsepower limitations. Some insurance
companies will not insure craft exceeding horsepower maximums and some
boat manufacturers will void any applicable warranties for the same reasons. http://www.dbw.ca.gov/pubs/ABC/ABCFull.pdf