Although you carry a C-card, you’re still subject to
dive operator scrutiny — can you attach your regulator
to your tank in three or fewer tries? They also expect you
to follow their rules, which is fair enough, as long as they
tell you their rules. We don’t have much regard for operators
who employ arbitrary rules that they announce and
enforce only after you’ve paid up and climbed aboard.
Last year Tim Lewis (Portland, OR) and his family visited
  Maui in Hawaii where his 17-year-old daughter completed
  an open water class and was issued a temporary
  proof of certification until her final card came from PADI
  headquarters. Days later, the family was aboard the Pride
  of Maui, says Lewis. The divemaster said he would not accept newly trained divers as the temporary c-cards were
worthless, mere souvenirs and not meant to grant diving
privileges. Three new divers were only allowed to snorkel.
Lewis argues: “If the organization felt that these temporary
  cards are invalid, they should be honest enough to
  placard their pier, their vessel, and their brochures with
  this. This is especially true Hawaii, where so many people
  get their initial training.”  
To announce a disqualification once someone is
  onboard, is deceitful, at best. While a C-card isn’t always
  an automatic ticket to dive, a good divemaster should
  think like George Purifoy, owner of Olympus Dive Center in Morehead City, NC. He told Undercurrent: “We pay
more attention to the way divers suit up and the questions
they ask than what cards they carry.”
Similarly, William Maley (Laguna Niquel, CA) booked
  a trip to Farnsworth Banks on the dive boat Atlantis out
  of Huntington Beach, CA. Once underway, says Maley,
  the captain announced that “he would not take us there
  because this was an advanced dive and three divers did
  not have advanced certification cards.” Log books were
  not sufficient to convince the captain. After a divemaster
  agreed to escort the three, the captain claimed the weather
  was too rough, which Maley thinks was a ruse. Since
  when has an advanced diver card been required for an
  advanced dive, especially since one can go directly from
  basic certification to advanced with little if any additional
  experience? It’s outrageous for a dive operator to enforce
  such a policy without disclosing it in advance.  
A more enlightened policy is offered by Peace
  Scuba, which operates a live-aboard out of Ventura, CA.
  Instructor Autumn Cleverley told Undercurrent that as oil
  rigs and outer islands are advanced dives due to strong
  currents and reduced visibility. When divers book a trip
  for the first time, a Peace staffer asks their level of experience
  — they want at least 50 dives in California waters. We
  take them at their word,” says Cleverley, but divers are also
  warned that divemasters will observe them and may bench
  them if they notice problems.  
Bud Worsham, proprietor of All About Scuba
  (Fairfield, CA) told us about a customer who was prevented
  from diving on a cruise when he admitted he hadn’t
  dived for more than a year. “Our shop is now advertising
  a refresher course to help prevent that happening again,”
  says Worsham. While there’s no industry rule, several
  training agencies recommend refresher courses every 12
  months. Certainly an operator can establish a rule, but
  he’s got an fiduciary obligation to inform a diver before hand — it’s unethical to take his money, then shut him
down. And what’s sacred about 12 months? Compare a
diver with 500 dives under his belt who hasn’t been wet
for a year with one who got certified six months ago and
hasn’t dived since. Different stories, for sure. Nonetheless,
when you arrive at a dive location you may be asked when
you made your last dive and if the operator believes it was
too long ago, your diving might be affected.
Deborah Lyon was on an Aqua Safari boat in Cozumel
  when a divemaster tapped a passenger on the elbow, “and
  asked him to leave the boat.” The captain had received
  a radio report that the diver had been drunk at a cafe
  the night before and the company felt it was not in his
  best interest to dive. He was assured the price of the dive
  would be refunded. He was disgruntled, but left without a
  fight.” Lyon says “when a boat operator running on a thin
  margin will say ‘no’ to someone who’s a safety hazard,
  that’s the company I want to dive with.” 
Perhaps, but it seems that this guy was busted on hearsay..
  Says Lyon: “don’t push the limits on a small island
  where everyone’s related!”  
Yet, there are times that benching a rule breaker
  makes sense. Sharon Reeves (Capitola, CA) was diving
  with Anchorage Divers in Dominica last July when
  a certified diver argued about the need for a checkout
  dive. Finally, he agreed to get in the water, but refused
  to remove his mask, or perform any skills requested.
  Agitated and aggressive, he soon ran out of air on a shallow
  dive but didn’t signal to anyone. “Instead,” Reeves
  reports, “he grabbed his wife’s regulator and began
  breathing from it, leaving her searching for her own
  octopus. The divemaster refused to allow the couple to
  continue diving. I for one am very grateful.” But, it seems
  they shouldn’t have let him in the water when he balked
  at the skills test.  
Next month: How medical conditions bench divers