Belly rot can occur with any wet dirty bedding some poor snake is forced to lay on. You might mention to them I've seen a heck of a lot more rotten looking bellies coming out of pet store snakes than I've seen in personal collections.

According to them you should put a source of heat for your warm side OVER a big arse water dish to up your humidity. Okay so then your snake is therefore forced to lay in said water dish in order to get to that heat source and thermoregulate. Well isn't that just a nifty plan of action...jeeze...NOT!

Ignore them, listen to folks that make a lot more sense. Take any information you get online or in person with a grain of salt and a dose of common sense and make sure you check that information against what you know and what you can research independently. You won't go wrong that way.