Marine motor belts

How 'marine' are marine belts? Is it one of those items where if they tag it 'marine' they can charge triple, or is there actually any difference between the PCM and Ford/Motorcraft belts?
Not that I mind paying some extra, but the regular belts I can get here in town, PCM would have to come from the US, at extra time and extra extra cost.

Use a quality belt and you will be fine. Gates, Dayco and Goodyear are considered quality belts. Beware, all three companies make premium belts and entry level. The premium belts are a better product, they will last longer and stay quieter.
If Mercury Marine wants a private label Mercury belt they will call one of those manufacturers and get them to make it. It won't be anything special it will just have their name added to the belt.

Cheap belts have less of the good stuff in them.
Good belts have all the cording for strength at the top of the belt where it is the widest so they are the strongest. Many cheap belts put the cording dead center in the middle of the belt where it is exposed to more heat and is not as wide so the belt is a lot weaker.
Good belts have 3 to 5 layers of thinner cording at the bottom of the belt where it is very narrow. This cording is slip stock. When the belt is slammed under a load it will dig deep in the pulley and try and wedge there. Slip stock lets it slip quietly while the pulley picks up speed and then grabs quietly and does its job.
All this refers to standard old fashion V belts not the newer Poly Rib belts.
It costs more to make them right and they do perform better when made right regardless of what brand you buy.