Wow pretty strong reaction. I get your standpoint and dealing with customer is not always easy. Whether the criticism is fair or not, I would not expect this kind of reaction from a vendor. A lot of information missing here.
I have to disagree with that being algae from the poor quality macro photo. I do think his tank will see its share of algae issues if it is as sterile and environment as it seems it may be, but to me it looks like a digitate hydroid.
To the OP, to confirm it is a hydroid and not algae, does it retract to light or movement? Being an animal they usually will retract back into the rock if exposed to bright light for safety.