I think it's incumbent on the diver (especially when diving rental equipment) to check his equipment before each and every dive. Certainly you should check it closely before the first couple of dives after the regulator has been serviced, whether it's yours or a rental. I say this as a professional regulator service tech--I have mistakenly left the wire ties off regs I've serviced; it's dangerous to the divcer and damned embarrassing to me. I've left hoses loose, too. I think just about every competent service tech has done both a time or two in his/her career.
My sidekick and I run a QA check on the regs the other turns out in an effort to catch any boo-boos before they leave the shop. Our motto is it isn't a mistake if we catch it before the customer does. No egos here; safety first.
In my pilot training I learned that a major cause of minor mishaps (like gear-up landings) is an interruption in the pilot's routine at critical moments in the flight. The pilot tends to the interruption, continues his approach and wonders just before the sound of metal on concrete what that infernal horn is beeping for. The same applies to maintenance. I strive to rebuild every reg I touch in the same order as the previous ones. That way I'm less likely to omit a step and turn out an incomplete product. Why am I saying this? Because the most likely time for a regulator to malfunction is immediately after it's been serviced. People are human and they make mistakes. Take your just-serviced equipment to the local quarry or pool and dive it before you go on that big trip. Better to find a problem here than on the boat in Paradise. And if you must rent, check it over carefully before you leave the rental shop. Hoses tight? Are they in good shape? Mouthpiece secure? Purge cover secure?
Happy (safe) diving!
