sjt7:
I used to operate a wholesale firm - They are going to know this guy isn't a legit store when he orders 1 yellow tang, a 3" french angel and a clownfish. Basically, you can spot a hobbyist by the way they order - small orders, one or two of each species, very particular about size, no substitutions, asking about care information, etc.
There is no "business license" per-se that wholesalers ask for before doing business with you. If you have a registered business name, that is about all you need (in Michgian anyway). A sales tax license might be required by the wholesaler - not to "prove" you are a legit store, but to keep themswelves out of trouble because they aren't charging you tax. Anyone can register their business name - it means nothing to the wholesaler. What they care about is the size of the order and if there will be repeat business. A $200 order from a hobbyist one time just isn't enough for legit wholesalers to bother with - they want customers who spend $1000 per week. Don't forget - just like there are "fake" retail stores, there are "fake" wholesalers - and these are the people working out of their garages and basements who are the ones most likely to sell direct to a hobbyist.
Jay