I'm not sure why this happens, maybe it's just human nature, but most people don't ask advice even from experts in a given field. Or maybe people are just a bit intimidated or shy to approach an expert.
Experienced belly dancers are flattered when you ask advice from them. Yes, very flattered! So do ask. It makes them feel good that you think highly enough of them to ask their advice.
Maybe its movement technique advice, or how you choice your music, or your costuming. The best way to ask is in person, but when you can't do that pick up the phone or email. Be sure to pay them a compliment. Who the heck doesn't like compliments? You could make their day! As a matter of fact they could be having a down day and you'll be the "pick me up" they need. And trust me, they won't forget you either.
So when in doubt, go ahead and ask their advice. Both of you will benefit.