simply a situation that can be solved at booking by taking two seconds to say "I dive doubles is that a problem?" ... When they state their policy you make adjustments according to your desires.
all I'm saying, making sure the op allows use of certain gear is OUR responsibilty not theirs.
Nope. I will ask if they have any unusual rules, but I never specifically ask about doubles. Any operator having unusual restrictions is obligated to disclose those restrictions. No deco diving, be on the boat with at least 500 PSI are common restrictions. Not allowing doubles is an unusual rule. In fact, I've never encountered it. I show up with two tanks, sometimes they are singles, sometimes twins. I've never had a problem. Usually, my twins even fit nicely into slots designed for two singles. I was on a boat Sunday morning that had a few slots designed for twins - sweet.