I trained the generative models all from scratch. Pretrained models are not that helpful when it's important to accurately capture very domain specific features.
One of the classifiers I tried was based on zoobot with a custom head. Assuming the publications around zoobot are truthful, it was trained exclusively on similar data from a multitude of different sky surveys.
Usually, if there's a scam, someone's making money off it. This is them. They want to keep making money.