I don't think it is an uncommon policy to refuse sales of scuba equipment to uncertified divers, and I sense there is a misunderstanding here.
For one, your friend, the experienced diver, likely would not purchase a gift certificate from a store that they didn't like.
On a side note, why don't you borrow your friend's regulator for your class, you might learn a thing or two during the class that might help you in selecting a regulator for yourself.
It is very uncommon. Otherwise very few people would get dive gear for their birthday and Christmas. It's a stupid policy that only drives business away. But for me that's a good thing!